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'[EE] Google calculator (includes units)'
2005\10\06@112737 by Gerhard Fiedler

picon face
I was surprised to see that Google has a calculator built-in. It can also
do calculations with units...

For the ones suffering from conversion pain (as the USA is moving slowly
but steadily to join the rest of the world on the metric side), maybe it
helps every now and then.

Try http://www.google.com/search?q=2+hours+*+40+btu+%3D
Or http://www.google.com/search?q=20+miles+in+km

It's not too smart with units... for example it doesn't seem to know how to
use US antique units for torque (lbf in, in lbf, lb in, in lb, etc. :) and
force (lbf for example). But some things still work.

Gerhard

2005\10\06@130140 by Wayne Topa

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face
Gerhard Fiedler(spam_OUTlistsTakeThisOuTspamconnectionbrazil.com) is reported to have said:
> I was surprised to see that Google has a calculator built-in. It can also
> do calculations with units...
>
> For the ones suffering from conversion pain (as the USA is moving slowly
> but steadily to join the rest of the world on the metric side), maybe it
> helps every now and then.
>
> Try http://www.google.com/search?q=2+hours+*+40+btu+%3D
> Or http://www.google.com/search?q=20+miles+in+km
>

It also includes a very fast way to download .pdf files.  Saves a lot
of time over searching the Microchip/Maxim sites.

WTT
--
Error:015: Unable to exit Windows. Try the door.
_______________________________________________________

2005\10\06@155403 by Randy Glenn

picon face
It seems to know a lot about a lot of different EE-related units. It
was a great help when doing Electromagnetics homework - when getting
the right unit as an result often meant you were close to actually
getting the right answer.

On 10/6/05, Gerhard Fiedler <.....listsKILLspamspam@spam@connectionbrazil.com> wrote:
{Quote hidden}

> -

2005\10\06@215551 by Chen Xiao Fan

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flavicon
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Why people in the States still use those antique units is beyond me.
Even the British now uses the ISO units.

As for the google calculator, I'd better use a simple unit conversion
program or some real calculators who can handle quite some units.
Google Office, Google Map, Google xxx, Google yyyy, Google zzzzz,
what is google now?

Regards,
Xiaofan

-----Original Message-----
From: Gerhard Fiedler
Sent: Thursday, October 06, 2005 11:28 PM

Try http://www.google.com/search?q=2+hours+*+40+btu+%3D
Or http://www.google.com/search?q=20+miles+in+km

It's not too smart with units... for example it doesn't seem to know how to
use US antique units for torque (lbf in, in lbf, lb in, in lb, etc. :) and
force (lbf for example). But some things still work.

Gerhard

2005\10\06@224131 by Russell McMahon

face
flavicon
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> Google Office, Google Map, Google xxx, Google yyyy, Google zzzzz,
> what is google now?

All things to all men (and women) that by all means they may win some.
If I may quote appropriately but entirely out of context.


       RM

2005\10\07@005559 by liam .

picon face
My favorite conversion program is called "Convert" (funnily enough..)

It knows about more units than I seem to ever need. And you can even
add your own custom unit conversions.

http://www.joshmadison.com/software/convert/



Liam

2005\10\07@053759 by Vasile Surducan

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On 10/7/05, liam . <liaaam2spamKILLspamgmail.com> wrote:
> My favorite conversion program is called "Convert" (funnily enough..)
>
> It knows about more units than I seem to ever need. And you can even
> add your own custom unit conversions.
>
> http://www.joshmadison.com/software/convert/

It could convert current density into a copper conductor from the US
standard into the EU standard ?

:)
cheers,
Vasile

2005\10\07@055912 by Alan B. Pearce

face picon face
>Why people in the States still use those antique
>units is beyond me.
>Even the British now uses the ISO units.

Sometimes.
Distances are still in miles, feet, inches etc, although engineering seems
to have essentially moved to metric.

Fuel is dispensed in litres, but people do still seem to talk about the
price per gallon. Some petrol station forecourt signs gave the price per
gallon, but with the recent price hikes I suspect they will have changed to
litre pricing to get the numbers reasonable. I still buy milk in pints, but
there have been prosecutions of stall holders and shop keepers who insist on
selling meat and vegetables in imperial weight units instead of metric -
they are supposed to sell in metric, and may have the imperial as a
secondary display.

2005\10\07@094834 by Gerhard Fiedler

picon face
Chen Xiao Fan wrote:

> Why people in the States still use those antique units is beyond me.

For me, the real question is why they insist on using multiple sets of
units/measures at the same time. In general, the US culture seems to value
efficiency, but when it comes to measuring systems, this definitely doesn't
hold true.

For an observer of the issue, it seems obvious that sooner or later they
will end up using all metric, just as (most) everybody else. Why exactly
they prolong this transition period for so long -- now over fifty years --,
that's what really is beyond me. Every country that's now using the metric
system had a transition period, but most of them kept that quite short.
Maybe it's just a general lack of understanding of the SI system... I don't
know, and can't figure it out :)

Gerhard

2005\10\07@102354 by Padu

picon face
From: "Gerhard Fiedler"
{Quote hidden}

I believe it has something to do with the fact that they call footbal a
sport they play with their hands.

:)


2005\10\07@103141 by Ling SM

picon face
>>Why people in the States still use those antique units is beyond me.
>
>
> For me, the real question is why they insist on using multiple sets of
> units/measures at the same time. In general, the US culture seems to value
> efficiency, but when it comes to measuring systems, this definitely doesn't
> hold true.
>
> For an observer of the issue, it seems obvious that sooner or later they
> will end up using all metric, just as (most) everybody else. Why exactly
> they prolong this transition period for so long -- now over fifty years --,
> that's what really is beyond me. Every country that's now using the metric
> system had a transition period, but most of them kept that quite short.
> Maybe it's just a general lack of understanding of the SI system... I don't
> know, and can't figure it out :)

I think not.  When I was there almost a decade ago, it took me quite
some months to realise the US definition of "the world series", but only
after looking very hard for quite a few times what other countries are
participating in the tournament.  I doubt you can change the "world"
overnight.

But then, why should others be trouble just for the conveniences of
science and standard.

Ling SM

2005\10\07@113054 by Xiaofan Chen

face picon face
Singapore used to be a colony of GB. And here people are generally
using metric units. However square metres (metres in US English)
and square feet are both used in property market. Petro (gas
in US English) and milk are in litres (liters) here.

In mechanical engineering and PCB design, inch or inch related
units (mil) are still used. Non-SI units like ounce are still used in
trading of gold. Traditions are really hard to break.

Chinese people are still using some non-SI units as well. For example,
"JIN" is a popular weight unit which is equal to half kilo now. So when
the law was passed to use SI units (kg and g), all the shops
replaced "per JIN" with "per 500g". Until now I often translate the
units to "JIN" from per 100g (why they use this in Singapore is
also strange, maybe to make people feel better) or per kg.

By the way, Olin mentioned "sort out" is British English, is it true?
I do not know that a "lad" means a male person of any age
between early boyhood and maturity (http://www.m-w.com)
though.

I think here in Singapore people also uses soccer and not football
even though FIFA stands for the Fédération Internationale de
Football Association.

Regards,
Xiaofan

On 10/7/05, Alan B. Pearce <.....A.B.PearceKILLspamspam.....rl.ac.uk> wrote:
{Quote hidden}

>

2005\10\07@113932 by Timothy J. Weber

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flavicon
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Chen Xiao Fan wrote:
> Why people in the States still use those antique units is beyond me.
> Even the British now uses the ISO units.

I chalk it up to insular nationalism, laziness, and "Not Invented Here."
 Anyone imposing a change at the Federal level would meet resistance
back home.

I was in grade school in the brief span of years when the U.S. flirted
with metric, so my cohort knows what a centimeter is.  But I think few
people older or younger do, other than scientists/engineers and people
who travel elsewhere (which is a minority).
--
Timothy J. Weber
http://www.lightlink.com/tjweber

2005\10\07@145946 by Gerhard Fiedler

picon face
Timothy J. Weber wrote:

>> Why people in the States still use those antique units is beyond me.
>
> I chalk it up to insular nationalism, laziness, and "Not Invented Here."
> Anyone imposing a change at the Federal level would meet resistance
> back home.

Ok, I understand the thing with the Feds, and that's one of the parts that
I think most others have something to learn from the US: a certain
resistance against centralization is a good thing. But laziness? It's so
much more effort to work with the different measurement units...

> I was in grade school in the brief span of years when the U.S. flirted
> with metric, so my cohort knows what a centimeter is.  But I think few
> people older or younger do, other than scientists/engineers [...]

And that's exactly where the question sits. I believe that all scientists
in the US work with SI units, just like everywhere else. It's just too
cumbersome otherwise. But the engineers and technicians seem to think it's
fun to convert all day long between different units, send Mars rovers off
track, have two sets of tools and measurement equipment... I'm lazy, too,
and that's why I don't understand this :)

I'm participating in the mechanic design of a unit for the automotive
aftermarket. For what I understand, the US automotive industry uses metric
threads, nuts and bolts for quite some time now; only the older cars still
use other threads. So it would make sense to make this unit also all
metric, wouldn't it? Why would you want to have a mixture of M4 and 8-32
bolts in your shop if you have a choice? While looking at a bolt, the
difference is almost obvious for a trained eye. But when looking at a
threaded hole, it's not so clear. I don't see a single reason to continue
to use the UTS threads... Yet they do get used, despite the fact that every
car you're working on is basically metric. I don't know, but my laziness
goes the other way 'round...

Gerhard

2005\10\07@153916 by Mario Mendes Jr.

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I would have to say that companies will do it in order to meet a standard
and be done with.  Then they get to say "We're ISO XyZ123 certified" =)

But the general public is not a company and there is no boss to say "if
you don't use metric you're fired" =)

Here in the US, when you go to chemistry or physics class (and maybe even
biology), they teach you to use the metric system because the books use
it, but then you leave school and never use it again unless you happen to
work with it.

It is plain laziness if you ask me.  People say "I know what a mile is but
I have no idea of what a kilometer is."  That's no excuse, since you're
driving and the odometer tells you how far you have gone.  As far as that
aspect of it is concerned, it is just all numbers.  Do you actually care
about the quantity of milk in the bottle when you go to the store?  Do you
actually ask yourself how many quarts of milk you're going to drink  this
week or how many milliliters of soda you'll need for a party?  NO!  You
just walk up to the shelf and pick up the big bottle or the smaller one,
or a few of each.

Therefore, my conclusion is that it is plain simple laziness.  The same
thing that's getting the Americans bigger and fatter every year (including
myself) =)


-Mario

{Quote hidden}

> -

2005\10\07@153918 by Timothy J. Weber

face
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> And that's exactly where the question sits. I believe that all scientists
> in the US work with SI units, just like everywhere else. It's just too
> cumbersome otherwise. But the engineers and technicians seem to think it's
> fun to convert all day long between different units, send Mars rovers off
> track, have two sets of tools and measurement equipment... I'm lazy, too,
> and that's why I don't understand this :)

I totally agree!

But I think there are two kinds of laziness: long-term and short-term.
Long-term laziness is the kind that will allow some short-term effort to
be expended for the sake of long-term efficiency.  It's the smart kind
of laziness.  Short-term laziness is the avoidance of any extra effort
at any moment.

I do think that current American culture is focused on the short term,
at the levels of government policy, corporate culture, and national
psyche.  The epidemic of obesity, refusal to conserve energy or natural
resources, other off-topic geopolitical issues that I will avoid here
:), corporate emphasis on quarterly stock performance, local government
trends such as sacrificing infrastructure stability for the sake of
brief sales tax revenue... and avoiding the cost of a one-time switch to
the rest of the world's standard units.  It's all short-term thinking to me.

And I don't think it's that individual American engineers are too lazy
to switch to metric, so much as that American corporations tend to have
that short-term laziness in their culture.  And for this issue, it's
industry that drives government to make the regulations that will change
industry; Congress isn't just going to make the change on its own.
--
Timothy J. Weber
http://www.lightlink.com/tjweber

2005\10\07@161358 by Herbert Graf

flavicon
face
On Fri, 2005-10-07 at 15:39 -0400, Mario Mendes Jr. wrote:
> But the general public is not a company and there is no boss to say "if
> you don't use metric you're fired" =)

You're right, there is no "boss" that can fire them. But there is
government.

In Canada, when we switched to the metric system the government simply
said "make it so". Road signs were switched, gas stations were switched,
food containers were switched, etc. (not overnight of course).

This left the public a choice: stick to the old units, always
converting, or get used to the new units.

These days many things in Canada are metric, with the odd occurrence of
the "old" system of units. For example: tires still have a small amount
of "imperial": 205/75R14, the first number is metric, the second a
ratio, the third is inches.

Weight of people is also something mostly still imperial.

And of course, anything closely tied to the states is still imperial.
Things like building supplies (yes we have 2x4s) are still often found
in imperial sizes.

It's actually kinda nice having mostly one system, but still being
exposed to the other, it prepares you for travel. In Europe a high of
25C is completely within my understanding. In the US a low in the 40s is
not as "comforting", but I'm familiar enough with it to understand it.

TTYL

-----------------------------
Herbert's PIC Stuff:
http://repatch.dyndns.org:8383/pic_stuff/

2005\10\07@165614 by Harold Hallikainen

face picon face
Interesting discussion! I'm still designing my circuit boards in inches
and constantly dividing mm on datasheets by 25.4 . My board layout
software supports dimensioning in mm. I haven't tried that, though. What
does a metric Gerber file look like? Are the dimensions converted to
inches, or is their a header saying the dimensions are in mm (or um?)?

Harold

--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\10\07@165632 by Mario Mendes Jr.

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> You're right, there is no "boss" that can fire them. But there is
> government.

Now, see... that's where I would agree with you.

That IS, but one of the many jobs of the government.  But in America, the
land of the free, where you cannot buy a beer on your birthday because
your ID happens to have your birth date as the expiration date, even when
your hair has gone gray and mostly gone from your head (but I was able to
buy a pack of cigarettes at the same place right after being denied a six
pack), the government is said to have only one job, and that is to protect
the people (and go to war for oil, of course, because after all, we are
protecting ourselves from having to, god forbid, walk once in a while) and
that's that!

We have no time to changes that make sense around here.  How dare you
suggest the government spend time and money on something that would make
us more aligned with the rest of the world?!!  Outrageous!  We already
have little time to deal with our frivolous law suits and watch TV as it
is =)

-Mario (neither a democrat nor a republican, just like to rant a lot =).

2005\10\07@165716 by Bill & Pookie

picon face
I agree fully about the short term planning of some business.

But to find the reason the public has not converted it is  necessary to
consider the Cowboy Culture and the Cowboy Way.

"That'll be the day, pilgrim" when John Wayne says "Reach for that gun and
you'll be 183 centimeters under."

Pookie

> I do think that current American culture is focused on the short term,
> at the levels of government policy, corporate culture, and national
> psyche.  The epidemic of obesity, refusal to conserve energy or natural
> resources, other off-topic geopolitical issues that I will avoid here
> :), corporate emphasis on quarterly stock performance, local government
> trends such as sacrificing infrastructure stability for the sake of
> brief sales tax revenue... and avoiding the cost of a one-time switch to
> the rest of the world's standard units.  It's all short-term thinking to
me.

2005\10\07@172203 by Timothy J. Weber

face
flavicon
face
Bill & Pookie wrote:
> But to find the reason the public has not converted it is  necessary to
> consider the Cowboy Culture and the Cowboy Way.
>
> "That'll be the day, pilgrim" when John Wayne says "Reach for that gun and
> you'll be 183 centimeters under."

True.  Even "two meters under" sounds too sissy-fied for a manly man.

And he certainly wouldn't wear a 37.85-liter or even a 40-liter hat.
--
Timothy J. Weber
http://www.lightlink.com/tjweber

2005\10\07@174021 by Harold Hallikainen

face picon face

> I agree fully about the short term planning of some business.
>
> But to find the reason the public has not converted it is  necessary to
> consider the Cowboy Culture and the Cowboy Way.
>
> "That'll be the day, pilgrim" when John Wayne says "Reach for that gun and
> you'll be 183 centimeters under."
>
> Pookie


Do you, in the rest of the world, use centimeters much? I REALLY like
keeping the metric prefix representing an exponent that is a power of 3.
So, I'd say "1.83 meters under" or probably round to 2 meters (metres)
under. So... how much do you use centi, deci, deka, etc. instead of just
going with milli? In electronics, we don't use centiamps!

Harold

--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\10\07@174327 by Bill & Pookie

picon face
Nor plug them with his trusty 11.176mm

pookie

----- Original Message -----
From: "Timothy J. Weber" <EraseMEtjweberspam_OUTspamTakeThisOuTlightlink.com>
To: "Microcontroller discussion list - Public." <piclistspamspam_OUTmit.edu>
Sent: Friday, October 07, 2005 2:22 PM
Subject: Re: [EE] Google calculator (includes units)


> Bill & Pookie wrote:
> > But to find the reason the public has not converted it is  necessary to
> > consider the Cowboy Culture and the Cowboy Way.
> >
> > "That'll be the day, pilgrim" when John Wayne says "Reach for that gun
and
> > you'll be 183 centimeters under."
>
> True.  Even "two meters under" sounds too sissy-fied for a manly man.
>
> And he certainly wouldn't wear a 37.85-liter or even a 40-liter hat.
> --
> Timothy J. Weber
> http://www.lightlink.com/tjweber
> --

2005\10\07@174714 by Bob Barr

flavicon
face
On Fri, 7 Oct 2005 13:56:12 -0700 (PDT), "Harold Hallikainen" wrote:

>Interesting discussion! I'm still designing my circuit boards in inches
>and constantly dividing mm on datasheets by 25.4 . My board layout
>software supports dimensioning in mm. I haven't tried that, though. What
>does a metric Gerber file look like? Are the dimensions converted to
>inches, or is their a header saying the dimensions are in mm (or um?)?
>

There are two Gerber header lines:

MOIN*  (for inches)

and

MOMM* (for millimeters)

which specify the measurement system that's applicable for that Gerber
file.

There's another statement ('Format', the 'FS' line) that specifies
leading or trailing zero suppresion and where the decimal point is
presumed to be.


Regards, Bob

2005\10\07@182000 by Harold Hallikainen

face picon face

>
> There are two Gerber header lines:
>
> MOIN*  (for inches)
>
> and
>
> MOMM* (for millimeters)
>
> which specify the measurement system that's applicable for that Gerber
> file.
>
> There's another statement ('Format', the 'FS' line) that specifies
> leading or trailing zero suppresion and where the decimal point is
> presumed to be.
>


Excellent! I wonder what happens if I send Advanced Circuits a mm based
Gerber file?

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\10\07@204707 by Bob Barr

flavicon
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On Fri, 7 Oct 2005 15:19:51 -0700 (PDT), "Harold Hallikainen" wrote:

<snip>

>
>
>Excellent! I wonder what happens if I send Advanced Circuits a mm based
>Gerber file?
>

I wouldn't expect that would be a problem. To confirm this, you might
want to use their free DFM check at http://www.FreeDFM.com

You do have to register but their site allows you to submit zipped
Gerber files for an error check. You get two emails back very shortly
after you upload your file - one has the error report and the other
has a quote for fabbing the board. It's a very nice system.


Regards, Bob

2005\10\08@063508 by Gerhard Fiedler

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Mario Mendes Jr. wrote:

>> You're right, there is no "boss" that can fire them. But there is
>> government.

> How dare you suggest the government spend time and money on something
> that would make us more aligned with the rest of the world?!!  

Actually, they do. The NIST has a nice site on the SI system, and it is, in
fact, the legal measurement system in the USA.

Home page of the units part: http://physics.nist.gov/cuu/Units/index.html

History of metrics in USA and legal context:
http://ts.nist.gov/ts/htdocs/200/202/5425.htm

And for me, it's not about alignment with the rest of the world, it's about
alignment within my own calculations :)  I never understood how someone can
put up with a unit conversion factor between electric power, mechanic power
and thermal power (for example). And that's something we (or at least some
of us) use quite frequently.

Gerhard

2005\10\08@064536 by Gerhard Fiedler

picon face
Harold Hallikainen wrote:

> how much do you use centi, deci, deka, etc. instead of just going with
> milli? In electronics, we don't use centiamps!

I can't really speak for the rest of the world, but I can speak from some
thirty years experience with everyday life in Germany. The most common
length units in normal life are centimeter, meter and kilometer.

Millimeter is almost only used in technical contexts; a millimeter is just
too small for everyday life's issues. For small everyday lengths, the
centimeter is the unit of choice; you'd say for example "that shelf is
about two centimeters thick". You probably use centimeter in similar
contexts as you'd use inch in the USA. Above ten centimeters, you use
mostly multiples of ten, like in "that cupboard is eighty centimeters wide"
-- and it's understood that this is not usually 80+-1, it's something
between roughly 70 and 90 or so. The decimeter is known but I've never seen
or heard it being used outside of textbooks. Bigger than that, you use
meters, usually in a form that could be translated as "six meter thirty"
for 6.3 m. For distances of thousand meters or above, it's the kilometer.
Dekameter is probably largely unknown to the general public. The 1/2 is
still common ("three and a half meter") instead of 0.5, but other than
that, it's mostly decimal if you need to go to precisions higher than 1/2.
Rounding happens more in the numbers than in jumping units; you'd say that
your street block is 80 meters wide, or that it's only 300 meters to your
friend's house.

You are right for technical drawings -- here the normal micro, milli, kilo
are being used almost exclusively.

I've heard on occasion the argument that in the metric system the numbers
are not round. That's just plain hogwash. Of course, if you want to express
3 1/2 inches in millimeters and calculate the /exact/ value of 3 1/2
inches, it's something that has usually one decimal of a millimeter -- not
really a "round" number (88.9 mm). But if you consider that the 3 1/2
inches are in reality 3 1/2 inches +-1/4 inch, for example, then you surely
can find a centimeter value within that range that is as "round" as "3 1/2"
-- try nine, which is what you probably would come up with if you started
out estimating in centimeters. And there's not much difference whether you
call that log a two by four or a five by ten; it's neither 2 by 4 inches
nor 5 by 10 centimeters anyway :)

Gerhard

2005\10\08@102026 by William Chops Westfield

face picon face
On Oct 8, 2005, at 3:34 AM, Gerhard Fiedler wrote:

> it's not about alignment with the rest of the world...

In the US, I suspect the failure to 'convert to the metric system' is
largely due to the cost of converting the industrial infrastructure.
It's not enough to have people understand the metric system and be
able to use it (arguably, we've DONE that, and all people need is
practice), unless you want to forever be using 6.35mm*1.27t/mmm bolts
and such silliness.  You have to convert ALL of that over.  And you'd
probably have to keep all the old stuff as well, for repair an
maintenance
of older equipment.  And since WW2, the US has had the largest
industrial
infrastructure in the world; with incredible momentum and probably
nearly
impossible (at least horribly expensive) to "convert" to anything.
The best we could ever hope for is some horrible kludge hybrid of metric
and old units that would have few of the advantages attributed to metric
and ALL the conversion problems we had before plus new ones.
(Just imagine trying to change all your electronics designs from
their 2.54mm pin spacing to 2.5mm pin spacing, for instance.)  Sigh.

Not that there hasn't been progress.  Booze comes in metric sizes these
days, and most soda.  Of course it's real annoying that things like
IC pin spacing didn't convert to metric much earlier; I would think that
in the SOIC timeframe at least, 1.5mm might have been doable, and WTF
did 0.07 inch "Shrink DIP" come from!!

Science and engineering in school is done pretty much exclusively in
metric in the US, I think (it was when I went to school, anyway.)  It's
only when you get to the real world that things get messy.  (hmm.
wouldn't
it have been nice if the meter had been picked so that 1g==10m/s^2
instead
of that "tiny fraction of long distance" thing?)

You see this sort of paradox all the time.  "Modern" isn't what happens
at the centers of innovation; they had to already be there to create
that innovation in the first place, so they're already out-of-date.
"Modern" is what happens when you HAVE the innovation and have to start
building something from scratch (Hmm.  New New Orleans might be
interesting.)  You might expect San Jose, CA to be a modern sort of
place,
being in the heart of silicon valley and all.  But it's not; SJ was
built
when the region surrounding it was largely agricultural, and it too big
to tear down and rebuild.  If you want modern, go to one of the nearby
areas that was farmland or slum during the agricultural days, and was
built AFTER "silicon valley" started to have influence on the world.
(or as another example, it was somewhat painful to watch my
cisco-supplied
ISDN internet connection fade from best-in-class to 'only 128kb?' as
people like my PARENTS bought COTS cable internet...)

BillW

2005\10\08@121706 by Tony Smith

picon face
In Australia, trades (like plumbers & carpenters) work in millimetres only.  Well, except for a few old codgers (and a few young
ones) who refuse to stop using inches.

Your 80cm shelf is referred to as eight hundred mm.  The old 6-foot is eighteen hundred, not 180cm or 1.8 metres.  And yes, if you
ask for a 6-foot piece of timber, it will be a bit short!  You need to ask for a piece eighteen thirty in length.

It also sorts out the amatuers from the pro's, if you ask for a 7.5cm pipe in the plumbing shop, you're not a plumber.

Tony


> {Original Message removed}

2005\10\08@133021 by Peter

picon face

On Fri, 7 Oct 2005, Harold Hallikainen wrote:

> Do you, in the rest of the world, use centimeters much? I REALLY like
> keeping the metric prefix representing an exponent that is a power of 3.
> So, I'd say "1.83 meters under" or probably round to 2 meters (metres)
> under. So... how much do you use centi, deci, deka, etc. instead of just
> going with milli? In electronics, we don't use centiamps!

Usually the cm is reserved for 'popular' use, about wherever you would
use inches people would use cm. E.g. timber and plank size, height of a
desk from floor, size of a window etc, in general low precision
carpentry and architectural stuff, packing boxes (cardboard) etc (the
spec for packing boxes is actually in mm but you will get odd looks if
you want one by mm in a shop). But it is never used for engineering
purposes or specifications, nor for machining. Those are in meters or
mm. F.ex. all screws and threads and drill bits are specified in mm. And
we NEVER use fractions for anything measurable, excepting the quarter,
the third and the half, in informal speech, usually in connection with
food weights or liquids.

Peter

2005\10\08@144847 by Gerhard Fiedler

picon face
William ChopsWestfield wrote:

> In the US, I suspect the failure to 'convert to the metric system' is
> largely due to the cost of converting the industrial infrastructure.

Hm... the US automotive industry converted to metric, quite some time ago,
I'm told. Probably about the same time they started to think about becoming
competitive and reducing cost (in the 70ies and 80ies).
The infrastructure seems to be there -- you can buy M3 screws just as
easily as you can by 4-40 screws. What seems not to be there is a general
consensus that it would make sense to use it...


> You have to convert ALL of that over.  And you'd probably have to keep
> all the old stuff as well, for repair an maintenance of older equipment.
> And since WW2, the US has had the largest industrial infrastructure in
> the world; with incredible momentum and probably nearly impossible (at
> least horribly expensive) to "convert" to anything.

I think by the time the conversion took place, that's what happened in most
other places. An infrastructure was in place, the old, inconsistent units
have been used in their respective markets, but people saw the advantage of
being able to talk to each other :)  The main difference, as I see it, is
that the USA is prolonging this intermediate state with multiple systems
for many decades now, over a century, as it seems inevitable that the US
industry will end up using metric (just like the US automotive industry).
I'm not sure that this is more cost effective. That sounds a lot like the
home owner who says he can't afford to fix the leak that costs him per
month twice in water costs of what the fix would cost...


> The best we could ever hope for is some horrible kludge hybrid of metric
> and old units that would have few of the advantages attributed to metric
> and ALL the conversion problems we had before plus new ones.

This is exactly what's happening now in the US. I think you should hope
(and shoot) higher... :)


> (Just imagine trying to change all your electronics designs from their
> 2.54mm pin spacing to 2.5mm pin spacing, for instance.)  Sigh.

There is an increasing number of metric spec'ed electronics parts. 0.8 mm
pitch, 0.65 mm pitch, 2 mm pitch etc. Many if not most newer cases are
spec'ed in metric units. Pretty much all cases that are spec'ed in
fractions of the King's toenails (I couldn't resist :) have also every
dimension given in mm in their specs. You don't have to change your designs
-- this seems one of the irrational thoughts that make this so difficult.
Just start to spec the new ones metric (128 mm x 68 mm instead of 5.04" x
2.68")... chances are that the majority of components on your boards are
spec'ed in metric unit by now anyway (if you use small SMT devices, at
least).

Ever wondered about some of the odd (in mil, that is) preferred drill sizes
that some board houses offer? Try converting these numbers to mm and you
see why :)


> (hmm. wouldn't it have been nice if the meter had been picked so that
> 1g==10m/s^2 instead of that "tiny fraction of long distance" thing?)
The "tiny fraction of long distance" is long past; now it's based on the
speed of light and a time AFAIK. Basing it on the gravity acceleration of
the Earth would be a bit problematic, I think, as this is probably not even
in a well-defined place as constant as they want the meter to be. I'm not
sure, but probably the tidal movement alone already creates a disturbance
in the gravity acceleration that's above the precision they use for the
meter.


> You see this sort of paradox all the time.  "Modern" isn't what happens
> at the centers of innovation; they had to already be there to create
> that innovation in the first place, so they're already out-of-date.
> "Modern" is what happens when you HAVE the innovation and have to start
> building something from scratch
I'm not sure what you're talking about here. It sounds as if you're
insinuating that the industrialized countries that are metric now had it
somehow easier, picking up this innovation from the USA, where it was
invented, building their infrastructure on it. If it is that, this is not
true in pretty much all aspects.
The SI and its predecessors that it is based on (like CGS and MKSA) have
been developed at least as much in Europe as in the USA, if not more so.
The SI itself is definitely a European "invention". So the "center of the
innovation" was as much (or more) Europe as it was the USA. Check out:

- CGS (proposed in 1830 by Gauss, later extended by Weber, Maxwell and
Thomson, all European). This is the first proposal of a consistent
measurement system.
http://en.wikipedia.org/wiki/Centimetre_gram_second_system_of_units

- Convention du Mètre: In 1875, 17 nations signed this treaty, among them
the USA. http://en.wikipedia.org/wiki/Convention_du_M%C3%A8tre

- Between 1900 and 1940, Giorgi (another European) and others developed the
MKSA system (meter, kilogram, second, ampere), that already resembled
closely the current SI. http://tinyurl.com/c9g4l

- Finally, in 1960 the current SI was introduced, based mainly on the MKSA
system, extending it in the same spirit and making its use consistent.
http://en.wikipedia.org/wiki/SI

As you can see, this was not a one-point-in-history thing; this was a
development that took over a century to culminate in the SI. During this
time most European countries (which had a quite developed infrastructure,
mind you, and were harboring most of the "inventors" of this system) slowly
moved over their infrastructure according to the insight that this system
makes sense.
And then the "building from scratch" aspect also doesn't hold. Conversion
to metric happened in Europe mostly between 1850 and 1950 (roughly). I
don't think you can seriously claim that the USA was much more
industrialized than Europe in that period. All industrialized European
nations had an infrastructure similar to the US at the time. The effort to
move to the metric system and to unify the various measurement systems in
use was not less than it would have been in the US -- at the time.
So, yes, in this context "modern" (the general use of the SI) is what
happens at the "center of innovation" (Europe, where this innovation has
been developed).

Gerhard

2005\10\08@150805 by Denny Esterline

picon face
> > (hmm. wouldn't it have been nice if the meter had been picked so that
> > 1g==10m/s^2 instead of that "tiny fraction of long distance" thing?)
>
> The "tiny fraction of long distance" is long past; now it's based on the
> speed of light and a time AFAIK. Basing it on the gravity acceleration of
> the Earth would be a bit problematic, I think, as this is probably not
even
> in a well-defined place as constant as they want the meter to be. I'm not
> sure, but probably the tidal movement alone already creates a disturbance
> in the gravity acceleration that's above the precision they use for the
> meter.
>

I _am_ sure :-)

Not so much tidal movement, but that which causes tidal movement. The
relative movements of the sun/moon and other planets can cause nearly 1%
variation in local 'g' over time. I don't have the numbers handy, but there
is also a significant variation dependant upon altitude. So much that
high-end 'g' meters can discern a few meters of altitude difference. Others
may weigh in here with more details but local gravity variations have long
been used as a tool for subterranean geological surveyors, like those used
to find oil.

-Denny

2005\10\08@194256 by Harold Hallikainen

face picon face
A recent post mentioned the CGS and MKS systems. It SEEMS to me that every
unit should just be based on the basic units, ie meter, not centimeter,
gram, not kilogram, etc. Why do we have CGS and MKS intead of MGS?

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\10\08@205938 by Xiaofan Chen

face picon face
The base unit for mass is kilogram not gram.

On 10/9/05, Harold Hallikainen <@spam@haroldKILLspamspamhallikainen.com> wrote:
> A recent post mentioned the CGS and MKS systems. It SEEMS to me that every
> unit should just be based on the basic units, ie meter, not centimeter,
> gram, not kilogram, etc. Why do we have CGS and MKS intead of MGS?
>
> Harold
>

2005\10\09@112618 by Gerhard Fiedler

picon face
Xiaofan Chen wrote:

> On 10/9/05, Harold Hallikainen <KILLspamharoldKILLspamspamhallikainen.com> wrote:
>> A recent post mentioned the CGS and MKS systems. It SEEMS to me that
>> every unit should just be based on the basic units, ie meter, not
>> centimeter, gram, not kilogram, etc. Why do we have CGS and MKS intead
>> of MGS?

> The base unit for mass is kilogram not gram.

The short answer is "it historic", the longer answer follows...


This is one of the (few) sort-of inconsistencies in the SI. What is
commonly called the "metric system" is actually a combination of a few
quite separate ideas or principles, that came into play at different times,
with different objectives.

There was first the meter (actually, the metre, but I confess I'm too
americanized to being able to use this spelling fluently :). A
socio-politico-scientific innovation of the French Revolution. The idea was
to put an end to the multiple standards that exist, and use only one
standard. In this sense, the USA is already "metricated", since
eighteenhundredsomething (found sources for 1866 and 1893) -- at least the
length and mass units that are being used in the USA (inch, foot, yard,
mile, pound) are defined in terms of the meter and the kilogram. There is
no independent standard for how long an inch is; it is defined (by the US
government) as being 0.0254 of whatever the SI meter is defined to be. In
this section, we have the origin of the meter, the gram, the second, the
liter -- the birth of a common standard for common measures.

The next idea behind the "metric system" is to use the same number system
for measures that we use in general for other numbers. All who can
immediately say (that is, in less than half a second) how many mils are
19/64th of an inch say "here" :)  There's a reason we use mils and not
binary fractions of inches in PCB design. To end this type of conversion
problem, it was agreed upon that people would use the decimal rather than
the binary system for fractions. Even though in many places that use the
metric system simple fractions like half and quarter are still common,
pretty much everybody knows how to transform them into the decimal number
system in under half a second :)  Other than that, measurements are treated
as numbers with a unit -- and for numbers, especially fractional numbers,
we all use in general the decimal system, so this was adopted for
measurements, too. The idea here is to make calculations with all measures
the same as calculations with other numbers.

Part of this is also the insight that we don't need different units for
different sizes; we can just use powers of ten to create a new unit that's
easy to convert. So instead of a mile with 1760 yards or 63,360 inches
(everybody knew that, right? :) we use a kilometer with 1,000 meters or
1,000,000 millimeters and things get /a lot/ easier.

These two ideas were part of what happened with a big bang during the
French Revolution, around 1790. This didn't start then and there, of
course; the underlying ideas had been floating around for a while by then.

The next idea is the discovery that most units can be seen as "derived"
units, from a system of base units. And here it becomes really interesting.
No matter whether you calculate energy in electric, mechanic, thermal,
whatever terms, you end up with joules (in the SI). So jules is as much
ampere•volt•second as it is newton•meter. Deeper analysis gets you to a
point where only a very few "base units" are needed, and all others are
defined in terms of these base units. The first steps here were the CGS and
MKSA systems. The use of the centimeter in the CGS system and the use of
the kilogram in the MKSA system are arbitrary, and partly due to the
technical possibilities of creating a standard base unit, convenience in
calculations and other factors. The thing is that at the time the
interrelationship between the units was discovered and widely explored, the
units themselves (like the gram or the kilogram) were already largely
defined. It is also not really relevant, for this aspect, what the base
units are -- as long as you use the same minimal set for all other units.
The base units for mass and length could be pound and inch, of course...
but then, BTU and watt wouldn't fit. The idea here is consistency between
all units.

The last idea behind the SI is the notion that it would be really good for
everybody if everybody used the same measurement system. So they took the
existing systems, analyzed them, enhanced them to cover areas so far not
included (for example the inclusion of the mole to bring chemical
calculations in the SI), and created one largely consistent system,
defining the use of base and derived units and decimal multiplication
prefixes. But the definition of the SI didn't happen in a vacuum, so to
speak, it happened considering all the existing systems and standards at
the time. So rather than creating a completely new standard based on meter,
gram, second, etc., they decided (in 1960) to stay within the already
widely used MKSA system and base the SI on the meter, kilogram, second,
ampere, kelvin, mole and candela. And we end up with that sort-of
inconsistency that the base unit for mass has a multiplicator prefix of
kilo, and the mass unit without any multiplicator prefix, the gram, is not
a base unit. But the multiplicator prefixes and the base units come from
different domains, so to speak, and are orthogonal concepts. Considering
this, it's not really inconsistent, just something to be aware of (in that
the newton for example is defined as m•kg/s and not m•g/s).

Gerhard


PS: If you think that "going metric" may be complicated, read section B.6
in this NIST document http://physics.nist.gov/Pubs/SP811/appenB.html. It
describes the complicated unit conversions the NIST defines to avoid "going
metric". I can't help it, but I don't see how it possibly could be cost
effective to hold on to this multitude of length units, and define and
redefine them over the decades in ever changing fractions/multiples of the
meter :)

2005\10\09@131949 by Peter

picon face

On Sat, 8 Oct 2005, Denny Esterline wrote:

> Not so much tidal movement, but that which causes tidal movement. The
> relative movements of the sun/moon and other planets can cause nearly 1%
> variation in local 'g' over time. I don't have the numbers handy, but there

The g variation over time is MUCH lower than 1% and in fact so hard to
measure that only some survey instruments pick it up. Lab instruments
are constantly checked by registering their daily readout variations
(mostly due to the moon) among other things.

Peter


2005\10\09@132335 by Peter

picon face

On Sat, 8 Oct 2005, Harold Hallikainen wrote:

> A recent post mentioned the CGS and MKS systems. It SEEMS to me that every
> unit should just be based on the basic units, ie meter, not centimeter,
> gram, not kilogram, etc. Why do we have CGS and MKS intead of MGS?

It's those men in Paris who did it.

Peter

2005\10\09@173440 by Harold Hallikainen

face picon face
THANKS for the EXCELLENT description of the history! The only place I
really end up dealing with MKS/CGS is when I teach a week on magnetics as
part of an introduction to electronics course. There are a fair number of
units in magnetics to begin with, then you get to double it to deal with
MKS and CGS. I sure like electronics where it's just meter - gram -
second.... But then I'm still designing circuit boards in mils
(milli-inches) and constantly multiplying and dividing by 25.4 to define
new footprints...

Harold


{Quote hidden}

>

2005\10\09@175727 by Gerhard Fiedler

picon face
Harold Hallikainen wrote:

> The only place I really end up dealing with MKS/CGS is when I teach a
> week on magnetics as part of an introduction to electronics course.
> There are a fair number of units in magnetics to begin with, then you
> get to double it to deal with MKS and CGS.

There shouldn't be any reason to use the CGS system today; it only has
historic relevance (as the first attempt to propose a consistent system of
units, which then developed into the SI). Why don't you stay with the SI
(which, for this purpose, is practically the MKSA system)?

Gerhard

2005\10\09@211342 by Harold Hallikainen

face picon face

> Harold Hallikainen wrote:
>
>> The only place I really end up dealing with MKS/CGS is when I teach a
>> week on magnetics as part of an introduction to electronics course.
>> There are a fair number of units in magnetics to begin with, then you
>> get to double it to deal with MKS and CGS.
>
> There shouldn't be any reason to use the CGS system today; it only has
> historic relevance (as the first attempt to propose a consistent system of
> units, which then developed into the SI). Why don't you stay with the SI
> (which, for this purpose, is practically the MKSA system)?
>
> Gerhard


I probably WILL stay with SI the next time I teach that class...

THANKS!

Harold

--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\10\10@062117 by Alan B. Pearce

face picon face
>I can't really speak for the rest of the world, but I can speak
>from some thirty years experience with everyday life in Germany.
>The most common length units in normal life are centimeter,
>meter and kilometer.
>
>Millimeter is almost only used in technical contexts; a
>millimeter is just too small for everyday life's issues.

Being a model railroader, I am always amused when I see drawings of
prototype locos and rolling stock with the overall length specified in
millimetres.

As an aside to this I find the 10:1 ratio of metric units results in too
many units to remember. I tend to work in millimetres and metres. Perhaps
this is due to the relative sizes of things I work on in the course of my
work, which requires close accuracy. If I was building furniture then maybe
I would work in decimetres, but for me to go from millimetres to decimetres
involves another round of calculation.

Maybe I'm too versed in the 1000:1 ratios used in electronic components.

2005\10\10@070541 by Alvaro Deibe Diaz

picon face
William Chops Westfield wrote:

[...]
> Science and engineering in school is done pretty much
> exclusively in metric in the US, I think (it was when I went
> to school, anyway.)  It's only when you get to the real world
> that things get messy.  (hmm. wouldn't it have been nice if
> the meter had been picked so that 1g==10m/s^2 instead of that
> "tiny fraction of long distance" thing?)
[...]

Historically, the meter was chosen so that it was well-related
to the second: an one-meter (ideal) pendulum, in a 1g condition,
and little displacement angle, has a period of oscilation of 1
second, no matter what weight you hang on it. Now the meter is
defined based in the distance the light covers in a determined
fraction of a second.

Alvaro Deibe.


2005\10\10@073849 by Alvaro Deibe Diaz

picon face
Gerhard Fiedler wrote:

[...]
> There's a reason we use mils and not binary fractions of inches in PCB
> design. To end this type of conversion problem, it was agreed upon that
> people would use the decimal rather than the binary system for
> fractions. Even though in many places that use the metric system simple
> fractions like half and quarter are still common, pretty much everybody
> knows how to transform them into the decimal number system in under half
> a second :)  Other than that, measurements are treated as numbers with a
> unit -- and for numbers, especially fractional numbers, we all use in
> general the decimal system, so this was adopted for measurements, too.
> The idea here is to make calculations with all measures the same as
> calculations with other numbers.
>
> Part of this is also the insight that we don't need different units for
> different sizes; we can just use powers of ten to create a new unit
> that's easy to convert. So instead of a mile with 1760 yards or 63,360
> inches (everybody knew that, right? :) we use a kilometer with 1,000
> meters or 1,000,000 millimeters and things get /a lot/ easier.
[...]

There were non-decimal numerical cultures in the past. We have rests of this
culture in, as an example, the time division: 60 seconds in a minute, 60
minutes in an hour, 24 (2x12, more exactly) hours in a day, 28,29,30 or 31
days in a month, and 12 months in a year. Asimov (and others) proposed a
much more rational calendar...

The number 12 was elected as the base in most of these systems. Here (Spain)
the eggs came in 6 or 12 unit crates, and we still use to gift a dozen roses
to the girlfriend. But, finally, the number 10 was selected as the best one.
And this is the most logical selection: our numbers come from the arabic
ones, and these from the Indian culture. They elected exactly ten glyphs to
represent ten numbers... because we have ten fingers in our hands, and the
fingers are the first "calculator", and the first tool we use to count. So,
our brain is especially prepared to use the number ten. And we have only 10
glyphs, so multiplying and dividing by ten is secon nature to us. Is like
having an special coprocessor to do the math related with the number 10.

We can do easily other kind of simple maths, like using binary fractions,
but we have ten numbers, and not two (like computers).

Finally, as an example of how the number representation can influence the
way we see maths and numbers, the number representations used by romans,
with all that I,X,L,C,D,M (and without 0!) did little favor to the
mathematical progress of the Roman Empire. Try to make some multiplications,
divisions or a "simple" square root in roman numbers. Good luck :o)


2005\10\10@100130 by olin piclist

face picon face
Alvaro Deibe Diaz wrote:
> Historically, the meter was chosen so that it was well-related
> to the second: an one-meter (ideal) pendulum, in a 1g condition,
> and little displacement angle, has a period of oscilation of 1
> second, no matter what weight you hang on it.

I thought that was a proposal favored by Thomas Jefferson, but was not
adopted.  Probably on account of he wasn't French enough.  Instead they
picked something like 1/10000 the distance from the north pole to Paris (I'm
sure I've got the particulars wrong), and grossly messed up the measurement
in the first place.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\10\10@134522 by Alvaro Deibe Diaz

picon face
Alvaro Deibe Diaz wrote:

>> Historically, the meter was chosen so that it was well-
>> related to the second: an one-meter (ideal) pendulum, in a
>> 1g condition, and little displacement angle, has a period
>> of oscilation of 1 second, no matter what weight you hang
>> on it.

Olin Lathrop wrote:

> I thought that was a proposal favored by Thomas Jefferson,
> but was not adopted.  Probably on account of he wasn't French
> enough.  Instead they picked something like 1/10000 the
> distance from the north pole to Paris (I'm sure I've got the
> particulars wrong), and grossly messed up the measurement in
> the first place.

Well, yes, and yes, and almost...

Most units evolve during its "useful" life. The meter, or metre, (metro in
Spain) born in 1670 in France (abate Mouton, bishop of Lyon). He suggest
using the length of an meridian arc equivalent to a minute of angle (don't
know if my english will be up to the task). This unit was called "mile", and
its fractions "virga" and "feet" (1/1000 and 1/10000 of a mile,
respectively). The length of the meridian was (is) not so simple to compute,
so Mouton showed how one could calculate these measures from a pendulum with
1 second period.

In 1671 Picard suggested using the length of the pendulum as the reference
of lengths. But the period of the pendulum varies with latitude, so in 1745
the French Science Academy proposes using the lenght of the 1-second-period
pendulum in the Equator as the measure basis.

Then, in 1790, with the French Revolution, Le Prieur proposes changing to
the length of the 1-second pendulum IN PARIS (yeah, really!). With this
measure in mind, a rule of Platinum-Iridium is forged, and stored in the
Louvre Museum. This become the meter standard (at 10ºC, of course) for a
long time. One third of this length was called feet, and the feet was made
up of 10 inches, with 10 "lines" in each.

In 1790 Talleyrand (again, bishop in Autun, France) proposes finding an
international solution to the lenght measure, and makes a "joint venture"
between the National Assembly and Sciences Academy (France) and the
Parlament and Royal Society (UK). The meter is defined in the length of the
1-second pendulum in a 45º latitude.

The problems with the latitude dependence of this definition of the meter
finally ended in 1792, when Borda, Lagrange, Monge and Condorcet suggested
using 1/4 of the length of an earth meridian. The meter was then defined as
10e-7 of this length.

The internationalization of the length measure grows, French,  English,
North American (contacts made with President Jefferson) and Spanish (Gabriel
de Ciscar, a scientific sended to Paris) try to measure the 1/4 of the
meridian 45. Finally, it was measured only a fraction of the meridian 45,
between Dunquerque (France) and Barcelona (Spain) both of them at sea level.

>From here, the definition of the meter changed as the science needed more
resolution, precision, repeatibility and stability than that of the
platinum-iridium in the Louvre museum. Definitions based in the speed of
Light, the wavelength of a red mark in the atomic spectrum of Cadmium
(1921), wavelengths of the radiation from a 86Kripton isotope in transition
between 2p10 and 5ds status(1960), the wavelength of "saturated absortion"
Lasers (1970) and, finally, the distance travelled by light in 1/299.792.458
seconds... (the circle finally closes again: the space measure is derived
from the time measure, just like in the 1-second pendulum).

The bottom line here is that the meter (and other units) evolved from a
propietary point of view to a more democratic measure, based on a nature
property, that can be measured everywhere, in the Earth and out of it. So
the meter have no property.

Sorry for the long mail. Hope it's not too much boring.

Alvaro Deibe.

2005\10\10@165738 by Peter

picon face

On Sun, 9 Oct 2005, Gerhard Fiedler wrote:

> Harold Hallikainen wrote:
>
>> The only place I really end up dealing with MKS/CGS is when I teach a
>> week on magnetics as part of an introduction to electronics course.
>> There are a fair number of units in magnetics to begin with, then you
>> get to double it to deal with MKS and CGS.
>
> There shouldn't be any reason to use the CGS system today; it only has
> historic relevance (as the first attempt to propose a consistent system of
> units, which then developed into the SI). Why don't you stay with the SI
> (which, for this purpose, is practically the MKSA system)?

Except that most molecular chemistry and such books use CGS. Argh.

Peter

2005\10\10@170139 by Gerhard Fiedler

picon face
William ChopsWestfield wrote:

> And since WW2, the US has had the largest industrial infrastructure in
> the world; with incredible momentum and probably nearly impossible (at
> least horribly expensive) to "convert" to anything.

Not sure how the USA infrastructure compares to Europe in that period. The
CIA Word Factbook estimates the current USA industrial production at $2.3T,
and the EU industrial production at $3.3T. That's about 50% more in the EU,
with the EU having about 50% more people (450M EU vs. 300M in the USA) and
about half the size of the USA. So comparing the USA to the part of Europe
that's today the EU doesn't seem to give a significant difference in depth
or breadth of industrial infrastructure. If anything, you could say that
the USA is less dependent on its industrial infrastructure: the percentage
of the GDP that comes from the industrial sector is 20% in the USA and 28%
in the EU.

Of course the US infrastructure is bigger than e.g. Belgium's, but I'm not
sure how this would be relevant in this context.

Also, by WW2 the "metrication train" had already left the station. The
right time for the transition would have been the century preceding WW2...
maybe starting right around the time when the US government defined the
inch as fraction of the meter (that was in the second half of the 19th
century!). This event could have told something to the attentive observer.


> (Just imagine trying to change all your electronics designs from their
> 2.54mm pin spacing to 2.5mm pin spacing, for instance.)  Sigh.

Ever noticed the small asterisk next to the column header "Millimeters" in
the dimensions table of most (if not all) Microchip case drawings?

When I designed my first circuit boards (late seventies), and for some time
after that, pretty much all available cases were specified in inches
(mils), and thus it made sense to use inch-based grids and units in PCB
design -- and so we did, even in otherwise all-metric Germany. Nowadays, it
seems that most cases are specified in mm -- but do designers in the USA
see it the same way we saw it back then in Germany, with the same
flexibility, and use metric units in their PCB design?

My guess is that many in the USA don't. There's probably a reason for that
difference, and that reason probably has something to do with the reason
why that train has left the station so long ago without the USA :)

Gerhard

2005\10\10@172122 by Peter

picon face


On Mon, 10 Oct 2005, Alvaro Deibe Diaz wrote:

{Quote hidden}

You mean two seconds for the pendulum, no ?

Peter

2005\10\10@172255 by Gerhard Fiedler

picon face
Alvaro Deibe Diaz wrote:

> The number 12 was elected as the base in most of these systems. Here (Spain)
> the eggs came in 6 or 12 unit crates, and we still use to gift a dozen roses
> to the girlfriend.

Yep, that's still pretty common, not only in Spain.

> But, finally, the number 10 was selected as the best one.

Not sure that selection came about because it was the best one, and there
are people who disagree with it being the best. But the fact is that it is
the one that pretty much everybody uses for pretty everything numeric in
calculations -- even when trying to figure out how much that product costs
in dollar per ounce :)

Gerhard

2005\10\10@172912 by Gerhard Fiedler

picon face
Olin Lathrop wrote:

> Probably on account of he wasn't French enough.  

Is this the deeper reason why this transition is so difficult? Because the
meter was "invented" in France? :)

I seem to remember that the USA and France were close allies at the time...

Gerhard

2005\10\10@202117 by William Chops Westfield

face picon face

On Oct 10, 2005, at 2:01 PM, Gerhard Fiedler wrote:

>> And since WW2, the US has had the largest industrial infrastructure in
>> the world; with incredible momentum and probably nearly impossible (at
>> least horribly expensive) to "convert" to anything.
>
> Not sure how the USA infrastructure compares to Europe in that period.

Thus the pick of WW2 as the starting point.  A lot of europe had to be
rebuilt AFTER WW2 (an ideal time for metrification), while much of the
US infrastructure I was alluding to was built FOR WW2 (and not
destroyed.)
(and building infrastructure on a war footing is a fine motivation
to do it wrong.)


> The CIA Word Factbook estimates the current USA industrial production
> at $2.3T, and the EU industrial production at $3.3T. That's about 50%
> more in the EU, with the EU having about 50% more people (450M EU vs.
> 300M in the USA) and about half the size of the USA.

Hmm.  Since what time do you think it appropriate to consider the EU
"unified" enough to count as one?  But... point taken.

>
>> (Just imagine trying to change all your electronics designs from their
>> 2.54mm pin spacing to 2.5mm pin spacing, for instance.)  Sigh.
>
> Ever noticed the small asterisk next to the column header
> "Millimeters" in
> the dimensions table of most (if not all) Microchip case drawings?
>
That's not the point.  If you're really metrified, you don't say "gee,
I think I'll design my chips with 1.27mm pin spacing.  That is NOT a
sensible metric "unit."  (arguably, 1/20 inch isn't so hot either, but
it's better.)  To truly metrify, you want all your grid intervals to
make sense in metric units.  You can SPECIFY metric units, and do layout
in metric units, but it's not really metrified...


> Also, by WW2 the "metrication train" had already left the station. The
> right time for the transition would have been the century preceding
> WW2.
>
Yes, that would have been nice.

> many in the USA don't [use metric units in their PCB design?]

I do when I use eagle.  Love those default track widths and drill sizes
like 1.016mm and such; that's part of what I'm talking about.  (Hmm.  I
changed my drill rack to nice even metric numbers; I guess I should do
the
trace widths too.)  Of course, I occasionally have to switch back to
english
units to do math on the grid :-(  (although I now have nice buttons to
multiply the grid setting by 2 or .5 at a single click, so I don't do
it as
much as I used to.)

BillW

2005\10\11@011559 by Russell McMahon

face
flavicon
face
>> Historically, the meter was chosen so that it was well-related
>> to the second: an one-meter (ideal) pendulum, in a 1g condition,
>> and little displacement angle, has a period of oscilation of 1
>> second, no matter what weight you hang on it.

AFAIR the meter was originally intended to be 1/10,000,000 th of the
distance from pole to equator on the meridian passing through Pairs
BUT the surveyors got it wrong. This was at Napoleon's time when the
power and pride of France were in ascendancy and a French based
"modern metric" unit was intended to add to France's prestige. BIMBW.

As noted by Peter 2 x Pi x sqrt( 1/g) ~~~= 2 where g ~~ 9.8 m/s/s.
(Or exactly 2 when Pi^2 = g :-) ).

>> Now the meter is
>> defined based in the distance the light covers in a determined
>> fraction of a second.

Last I recall it was actually N times the wavelength of a certain
emisison line of a certain gas (but they keep 'improving' these things
so ... ) :-)
1 metre = 2 cubits seems a much more sensible definition to me.


       RM

2005\10\11@034258 by Alvaro Deibe Diaz

picon face
>> Historically, the meter was chosen so that it was well-
>> related to the second: an one-meter (ideal) pendulum, in
>> a 1g condition, and little displacement angle, has a period
>> of oscilation of 1 second, no matter what weight you hang
>> on it. Now the meter is defined based in the distance the
>> light covers in a determined fraction of a second.
>
> You mean two seconds for the pendulum, no ?

That's right. I mean 1s is the the pendulum semiperiod. Sorry for the
mistake.

Regards,

Álvaro Deibe

2005\10\11@054030 by Alvaro Deibe Diaz

picon face
>> Historically, the meter was chosen so that it was well-
>> related to the second: an one-meter (ideal) pendulum, in
>> a 1g condition, and little displacement angle, has a period
>> of oscilation of 1 second, no matter what weight you hang
>> on it.

> AFAIR the meter was originally intended to be 1/10,000,000 th
> of the distance from pole to equator on the meridian passing
> through Pairs BUT the surveyors got it wrong.

Don't know what was wrong. The earth meridians still measure
about 40000000 meters nowadays... This is a negligible error,
bearing in mind that in 1687 Newton and Cassini were still
trying to decide the exact form of the Globe (then supposedly
spherical). (Equatorial length: 40.075Km; Meridian length:
40.008Km)

> This was at Napoleon's time when the power and pride of
> France were in ascendancy and a French based "modern metric"
> unit was intended to add to France's prestige. BIMBW.

In the france of the middle of sXVII the measure standards are
in hands of the established power (that was the case in almost
everywhere, of course). The measures are one more tool for the
power. Commerce, internal and with colonies, is based in them.
The French Revolution tried to "guillotine" all things related
to the then decadent power, and the measures system is no
exception. But the first attempt to construct a definition of
the meter based in natural properties was proposed in 1670
(Mouton), well before the French Revolution, and before
Napoleon. But, wait... That's it. Im am not sure I could
explain in english this kind of things, so here you have one
web link (obtained directly from St. Google, of course):

http://www.roma1.infn.it/~dagos/history/sm/node3.html

As you can see, the time measure is well defined in 1670, and
the pendulum is easily made everywhere. So it is an ideal first candidate to measure lengths.

In this web you'll find different names and dates, but it is a
logical result: my refferences are in Spanish and French, and
not in English    :o)

As a side note, fractions of a meridian were measured many
times, but well after the meter born: Maupertuis and Celsius
(Laponia, 1745), Jorge Juan and Antonio de Ulloa (Perú, between 1735 and 1744), Lacaille (Buena Esperanza, 1752) and many more
(from Italy and North America, basically).

Incidentally, Antonio de Ulloa and Jorge Juan were both from
Galicia, in the NorthWest of Spain, and Jorge Juan born in
Ferrol, the town were I live. This is my connection with the
SI...    :o)

> As noted by Peter 2 x Pi x sqrt( 1/g) ~~~= 2 where g ~~ 9.8
> m/s/s.
> (Or exactly 2 when Pi^2 = g :-) ).

Yes. It was my error. I mean 1s is the SEMIperiod of the
Pendulum. Sorry again.

{Quote hidden}

Well, things get faster and faster everyday. It may well be that my
informations are not up to date.

Regards,

Álvaro Deibe.

2005\10\11@072031 by olin piclist

face picon face
Russell McMahon wrote:
> Last I recall it was actually N times the wavelength of a certain
> emisison line of a certain gas (but they keep 'improving' these things
> so ... ) :-)

That was the previous standard.  With new more accurate atomic clocks
available the meter was redefined as the distance light travels in vacuum
during a specific time.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\10\11@074813 by Gerhard Fiedler

picon face
Russell McMahon wrote:

> Last I recall it was actually N times the wavelength of a certain
> emisison line of a certain gas (but they keep 'improving' these things
> so ... ) :-)

Yes, they do keep improving. It's now defined as the distance the light
travels in vacuum in 1/299,792,458 of a second. See e.g.
http://physics.nist.gov/cuu/Units/meter.html

> 1 metre = 2 cubits seems a much more sensible definition to me.

Well, seems you missed /that/ point of the French Revolution -- but since
you're a subject of the Royal Commonwealth, that's understandable :)

Gerhard

2005\10\11@092307 by Gerhard Fiedler

picon face
William ChopsWestfield wrote:

>>> And since WW2, the US has had the largest industrial infrastructure in
>>> the world; with incredible momentum and probably nearly impossible (at
>>> least horribly expensive) to "convert" to anything.
>>
>> Not sure how the USA infrastructure compares to Europe in that period.
>
> Thus the pick of WW2 as the starting point.  A lot of europe had to be
> rebuilt AFTER WW2 (an ideal time for metrification),
It is correct that much of it was rebuilt after WW2, but most of it got
rebuilt to the same standards that were there /before/ the war.

You seem to argue carefully besides the point here :) -- the point being
that by the time WW2 approached, the metrification in Europe was already
completed. The only development of substance that happened after WW2 was
the consolidation and enhancement of slightly different metric systems into
the SI. But as I explained in previous posts, the individual structural
elements that make up the SI had been in widespread use long before 1960
(birth of the SI) -- in Europe, of course.

As you say, it would have been nice for the USA to follow this lead more
closely.


>> The CIA Word Factbook estimates the current USA industrial production
>> at $2.3T, and the EU industrial production at $3.3T. That's about 50%
>> more in the EU, with the EU having about 50% more people (450M EU vs.
>> 300M in the USA) and about half the size of the USA.
>
> Hmm.  Since what time do you think it appropriate to consider the EU
> "unified" enough to count as one?  But... point taken.

It's not the point whether or how I consider them as unified. (IMO, partly
they are, partly they aren't.) The point is that you started out comparing
the USA to the world. Of course, in terms of a single country, the USA has
had (and probably still has) the biggest industrial infra of every country
since WW2. But the numbers per country don't really say that much,
especially not about metrification; numbers per people, or other relative
indicators are usually much more revealing, or comparing structures of
similar size. That's why I brought in the EU, as something better
comparable to the USA than Belgium or Greece.

You are correct in that they can't really be considered as "unified",
especially not during the period the metrification happened in Europe.
Which, in a sense, doesn't make a common metrification easier; one could
argue that a single country of comparable size and infrastructure has it a
lot easier than a bunch of loosely connected countries.


>> Ever noticed the small asterisk next to the column header "Millimeters"
>> in the dimensions table of most (if not all) Microchip case drawings?
>>
> That's not the point.  If you're really metrified, you don't say "gee,
> I think I'll design my chips with 1.27mm pin spacing.  That is NOT a
> sensible metric "unit."  (arguably, 1/20 inch isn't so hot either, but
> it's better.)  To truly metrify, you want all your grid intervals to
> make sense in metric units.  You can SPECIFY metric units, and do layout
> in metric units, but it's not really metrified...

When did you design your last SMD board? 50 mil pitch is already an "old"
case. Most newer chip cases use pitches of 0.5 mm, 0.65 mm, 0.8 mm.
Regarding my point in question, the Microchip PIC cases: the PICs with more
than 20 or so pins mostly don't come in mil-pitched cases at all. And those
smaller PICs that still come in 50 mil and 100 mil pitch cases also come in
smaller cases, usually with 0.65 mm pitch. (Side point: the mere fact of us
talking in mils rather than binary fractions of inches is already
introducing one of the structural elements of metrification.)

When you take any SMD PCB with recent components and look up the component
specs, I'm sure you'll find no good reason to stay with mils and inches.
Take for example the cases commonly known as 0603. In most specs, you'll
find that its size is spec'ed with 1.6 mm × 0.8 mm rather than 60 mil × 30
mil -- even when the case continues to be referred to as 0603 rather than
1608. I'm not sure you can come up with a single (current) datasheet where
the 0603 case is spec'ed as 60 mil × 30 mil; I haven't seen one in a long
time. The bigger capacitors (3216 and such) are all spec'ed and named in
metric units. So all the resistors and capacitors usually have metric
specs. The SOT cases are also spec'ed in metric units. For most of these,
it doesn't really matter whether you use inches or meter as base unit,
because the numbers are not really round in any system, but fact is that
the imperial measurements are merely calculated from the metric specs and
only given as convenience for the ones who are not able to or don't want to
work with the actual specs.

Let me clarify what "the point" is IMO:
- I'm talking about SMD or mixed boards that are at least somewhat designed
with space saving in mind, which probably are the majority of PCBs designed
today.
- The components used in these boards are in the vast majority specified in
metric units. There is the occasional 50 mil pitch SO case or maybe a
TO-220 with 100 mil pitch, but even these are usually spec'ed in metric
units now.
- If the spec'ed sizes are round numbers at all, they are in the majority
round numbers in metric units.
- Since the sizes and pitches of the footprints differ so much in a typical
design, there's no good reason for a routing or placement grid anyway. On
what grid would you place a 0.65 mm pitch TQFP case, 0603 resistors and a
100 mil header?
- Check out the material used for your boards. Chances are the thickness
and other properties are spec'ed in metric units, and imperial units are
given as convenience only.
- So what's the advantage of staying with imperial units for board specs?
Is there any? Or is it merely a certain mental laziness or a resistance to
do it the way everybody else (outside the USA, that is) does it?

The thing is, the electronic industry /is/ largely metric by now, also in
the US. But most of the datasheets of at least US companies still show size
measurements in inches, for reference only, as convenience for the ones who
can't deal with it. This kind of camouflages this fact, for the ones who
don't look closely. It's the same one can see in other areas: resisting is
just prolonging the suffering and final death of the imperial units :)


>> many in the USA don't [use metric units in their PCB design?]
>
> I do when I use eagle.  Love those default track widths and drill sizes
> like 1.016mm and such; that's part of what I'm talking about.  
See... of course, there will be the occasional oddity. But it doesn't
really matter whether you route with a trace width of 8 mil, 0.203 mm or
0.2 mm. The difference is simply cosmetics. And once the manufacturers of
ECAD programs get the word that everything is spec'ed in metric and most
people work in metric, the defaults will eventually come in metric, too.
May take a while, though... but these are not the only programs that come
with strange defaults :)


I found that up to 5 years ago, I rather frequently switched units and
grids between metric and imperial when creating footprints. But that
doesn't happen anymore -- there's no reason for it now. Ok, it's still
easier to draw a 50 mil pitch SO case on a 10 mil or 50 mil grid; but if
you have a spec'ed footprint, chances are you have all the metric
measurements right there. Not on a nice round metric grid, in this case,
but still... and it's the exception rather than the rule now. There are few
footprints that can be drawn on any grid (other than really small ones,
like 0.1 mm or 5 mil or 1 mil).

Even those old-timers like TO-220 cases... the distance between the outer
pins is spec'ed (in the one case I have in front of me, VPN49N04) with min.
4.95 mm and max. 5.15 mm. 5 mm is as much within this range as is 200 mil
(5.08 mm).

Gerhard

2005\10\11@122430 by Harold Hallikainen

face picon face
Nice discussion! I'm currently designing boards with a 10 mil grid (10 mil
trace width, 10 mil space). When I come up to a footprint, I hit a key
that snaps the trace over to the pad (using a 45 degree trace, then back
to horizontal or vertical). The grid makes it easy for me to maintain
clearances. So... if I do my next board in mm, what is the suggested grid,
trace width, and spacing? I just may give it a try!

Harold


--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\10\11@124132 by David Van Horn

picon face
> Nice discussion! I'm currently designing boards with a 10 mil grid (10
mil
> trace width, 10 mil space). When I come up to a footprint, I hit a key
> that snaps the trace over to the pad (using a 45 degree trace, then
back
> to horizontal or vertical). The grid makes it easy for me to maintain
> clearances. So... if I do my next board in mm, what is the suggested
grid,
> trace width, and spacing? I just may give it a try!

I'm doing everything here on 8/8. Works out nicely if your board house
supports it.


2005\10\11@130058 by Harold Hallikainen

face picon face

>> Nice discussion! I'm currently designing boards with a 10 mil grid (10
> mil
>> trace width, 10 mil space). When I come up to a footprint, I hit a key
>> that snaps the trace over to the pad (using a 45 degree trace, then
> back
>> to horizontal or vertical). The grid makes it easy for me to maintain
>> clearances. So... if I do my next board in mm, what is the suggested
> grid,
>> trace width, and spacing? I just may give it a try!
>
> I'm doing everything here on 8/8. Works out nicely if your board house
> supports it.


8mm seems a bit big! What metric grid are people using?

Harold

--
FCC Rules Updated Daily at http://www.hallikainen.com

2005\10\11@132058 by David Minkler

flavicon
face
Sounds like you would be comfortable at 0.25mm

Dave

Harold Hallikainen wrote:

{Quote hidden}

2005\10\11@135048 by Harold Hallikainen

face picon face
That looks reasonable... I'll try it on my next board!

Thanks!

Harold


{Quote hidden}

> -

2005\10\11@175242 by William Chops Westfield

face picon face
On Oct 11, 2005, at 6:22 AM, Gerhard Fiedler wrote:

> You seem to argue carefully besides the point here

Actually, I think we're arguing slightly different points.  I've been
trying to explain why the US, in spite of teaching the metric system
in the schools since the 1970s or so, still hasn't managed to actually
covert to metric.  You're arguing that in fact we SHOULD have converted
much earlier than the 1970s...

Well - I agree with you.  All I'm saying is that since we didn't convert
"earlier", it only got increasingly difficult to convert "later"...

BillW

2005\10\11@220222 by Gerhard Fiedler

picon face
William ChopsWestfield wrote:

>> You seem to argue carefully besides the point here
>
> Actually, I think we're arguing slightly different points.  I've been
> trying to explain why the US, in spite of teaching the metric system in
> the schools since the 1970s or so, still hasn't managed to actually
> covert to metric.  You're arguing that in fact we SHOULD have converted
> much earlier than the 1970s...

Actually, I might have come across more argumentative than I wanted to. It
was more an asking of why exactly it didn't happen -- not earlier, not
later. And why it is /still/ difficult for people to use M3 screws instead
of 4-40 screws... :)

Gerhard

2005\10\11@220628 by Gerhard Fiedler

picon face
Harold Hallikainen wrote:

>> I'm doing everything here on 8/8. Works out nicely if your board house
>> supports it.
>
> 8mm seems a bit big! What metric grid are people using?

I guess he's talking about 8 mils :)

I'm not working with a grid. I use design rules, specify the clearances,
and the program keeps me within the allowed limits.

But even with a grid, it's really not rocket science... you get the
clearance data from your manufacturer, and if it's in mil, you just
calculate what this comes out as in mm. If it's 8 mil, it's 0.2 mm, if it's
10 mil, it's 0.25 mm.

Gerhard

2005\10\11@223202 by Chen Xiao Fan

face
flavicon
face
I think we have a problem here since 10mil is more like 0.254mm
than 0.25mm. The error of this 0.004mm may not be a problem in
normal cases. 100mil is 2.54mm and not 2.5mm and the 40um error
can be a big problem for the SMD optical component placement
for us.

I just checked with my layout designer that he is using 0.255mm
for 10mil) since the SMD guys does not like the 0.004mm in the
0.254mm so that he rounds everything to 0.005. So 100mil will be
2.540mm and this has very small error. It seems to me that
it is still more convenient to use mil if the PCB board house
and the SMD machines accept mil.

Regards,
Xiaofan

{Original Message removed}

2005\10\12@091931 by Gerhard Fiedler

picon face
Chen Xiao Fan wrote:

> I think we have a problem here since 10mil is more like 0.254mm than
> 0.25mm. The error of this 0.004mm may not be a problem in normal cases.
> 100mil is 2.54mm and not 2.5mm and the 40um error can be a big problem
> for the SMD optical component placement for us.

I'm not sure I understand you. What is the connection of routing grids and
trace width to component placement? When I have components to place that
have position constraints (like connectors that get mounted to both the
board and a panel, or optical components), I don't position them on a grid
at all, I position them on their exact position -- be it specified in mm or
inches, without error in either case.

> I just checked with my layout designer that he is using 0.255mm for
> 10mil) since the SMD guys does not like the 0.004mm in the 0.254mm so
> that he rounds everything to 0.005. So 100mil will be 2.540mm and this
> has very small error. It seems to me that it is still more convenient to
> use mil if the PCB board house and the SMD machines accept mil.

I'm not sure, but I don't think there are many board houses or SMD machines
that don't accept files (Gerber, pick and place) in mm. I'm no expert in
board production, though... If, as you say, your SMD guys prefer 0.255 mm
to 0.254 mm, it seems to me that this is because they /don't/ work in mil
-- if they did, they'd prefer 0.254 mm, as it translates to a round mil
value, whereas 0.255 mm doesn't.

But I think I don't understand the problem you're describing at all -- like
what exactly the SMD guys do and what they don't like about 0.254 mm in
what they do, and what the 0.254 mm are that you are talking about.
Placement grid? Routing grid? Clearance?

Gerhard

2005\10\12@093154 by Xiaofan Chen

face picon face
The problem is that the PCB libraries are created in mil in the
headquarter in Germany and the local SMD machines and board
houses are using mm. Some of the old documentation are also
using mil but we are woking with mm now so we need to
translate mil to mm. What I am saying is that we need to convert
100 mil to 2.54mm and not 2.5mm.

Regards,
Xiaofan

2005\10\13@083640 by Gerhard Fiedler

picon face
Xiaofan Chen wrote:

> What I am saying is that we need to convert 100 mil to 2.54mm and not
> 2.5mm.

Exactly... that's what I do, too, and that's how it needs to be, when the
measures are exact measures.

But that doesn't necessarily apply when somebody is asking "I'm using a 10
mil grid now, what would be an equivalent metric grid?" The layout grid
size is mostly not a reflection of an exact measurement, it's a more
esthetic thing.

Gerhard

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