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'[EE:] scope timebase calibration'
2003\11\17@100643 by Hulatt, Jon

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Hi All,

I've finally bought me a scope. Hasn't arrived yet, but I've read the
instructions and I'm wondering what can I use for frequency calibration,
considering that I don't have a calibrated oscillator.

Would 50Hz mains AC be accurate enough for LF calibration? and is there a
fairly precise higher frequency waveform that I can use in or from something
else??

thanks

Jon

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2003\11\17@101441 by Olin Lathrop

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> Would 50Hz mains AC be accurate enough for LF calibration?

Depends on where you live.  In civilized parts of the world, the power
line frequency is controlled far more accurately than you can see on a
scope.

> and is there
> a fairly precise higher frequency waveform that I can use in or from
> something else??

Any crystal oscillator will be far more accurate than any error you can
see on a scope.


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2003\11\17@102104 by Rick C.

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Depends on the scope. Calibration is usually performed by an internal square
wave reference that is usually brought out on a terminal on a good quality
scope. This is all that's necessary for relative frequency calibration. There's
usually a (cal) position on the horizontal sweep control and a screwdriver
adjust to get the calbration close. This square wave is also useful for
adjusting the scope probe (capacitance) too.
Rick

"Hulatt, Jon" wrote:

{Quote hidden}

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2003\11\17@104603 by Hulatt, Jon

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> Depends on the scope. Calibration is usually performed by an
> internal square wave reference that is usually brought out on
> a terminal on a good quality scope. This is all that's
> necessary for relative frequency calibration. There's usually
> a (cal) position on the horizontal sweep control and a
> screwdriver adjust to get the calbration close. This square
> wave is also useful for adjusting the scope probe
> (capacitance) too. Rick
>

The manual states that the cal output(s) are only to be used for matching
the probes, the frequency is not reliable.

> > Would 50Hz mains AC be accurate enough for LF calibration?
>
> Depends on where you live.  In civilized parts of the world,
> the power line frequency is controlled far more accurately
> than you can see on a scope.
>

I live in the UK. I think we're pretty civilised here :o)

>
> Any crystal oscillator will be far more accurate than any
> error you can see on a scope.
>

Good point. My 20MHz crystals I run my pics on are alledgedly +- 50ppm. That
should probably do the trick.

Thanks for the pointers

Jon

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2003\11\17@110019 by Mike Singer

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Olin Lathrop wrote:
> Any crystal oscillator will be far more accurate than any error
> you can see on a scope.

  It's not that true, just feed X deflection channel of the scope
with the sine from the temp-compensated sine generator and
turn off synchronization.

>  ...In civilized parts of the world, the power line frequency is
controlled far more accurately than you can see on a scope...

Sorry, that's me who got restricted to be not free to comment
this kind of statements (perhaps due to I live in "wrong" i.e.
"uncivilized" from someone's point of view part of the world).

Mike :-)

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2003\11\17@111057 by David VanHorn

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>
>>  ...In civilized parts of the world, the power line frequency is
>controlled far more accurately than you can see on a scope...
>
>Sorry, that's me who got restricted to be not free to comment
>this kind of statements (perhaps due to I live in "wrong" i.e.
>"uncivilized" from someone's point of view part of the world).

The powerline frequency is only correct in the long term. (hours)

I remember watching our school clocks visibly slow, when the local steel mill fired up.

A canned crystal oscillator will give you a nice accurate timebase.
You can build one, but you'll need to get the xtal loading caps right before you'll get the right frequency..
You can compare a 10 MHz oscillator to the WWV carrier, using a shortwave receiver.
WWV broadcasts on 2.5, 5, 10, 15, and 20 MHz, but the 10 MHz is the most consistently easy to pick up, at least around here.  Take that 10 MHz canned oscillator, and divide it down by several stages of /10's, with socketed, buffered outputs, put it in a cabinet, and you have an nice reference generator.

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2003\11\17@112746 by Alan B. Pearce

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>Good point. My 20MHz crystals I run my pics on are
>alledgedly +- 50ppm. That should probably do the trick.

Think in terms of "a lot more accurate than you set the scope to" :))

The reality is that the calibration on screen is not very accurate at all,
even on the best scopes, unless you have a dso where the sample rate is
controlled accurately. But even then your ability to read the display is
much lower than the calibration accuracy.

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2003\11\17@113408 by Hulatt, Jon

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> >Sorry, that's me who got restricted to be not free to
> comment this kind
> >of statements (perhaps due to I live in "wrong" i.e.
> "uncivilized" from
> >someone's point of view part of the world).
>

I don't understand what you're saying?!?



> The powerline frequency is only correct in the long term. (hours)
>
> I remember watching our school clocks visibly slow, when the
> local steel mill fired up.
>

That's interesting, but suprising. Now, correct me if I'm wrong, but...

Every generator set that contributes to the grid has to be running in
perfect frequency and phase with the grid. Therefore, if immense loading on
the grid would slow down the frequency, it must correspondingly slow down
all of the connected generator sets and in turn, the turbines or engines
that drive them. Which seems odd.

Furthermore, since "anyone" can contribute supply to the grid, and can only
connect their generator set when it is perfectly in phase with the grid,
then how on earth can someone realistically expect to get their generator in
phase with a significantly changing frequency or phase?

Although, I could be getting the wrong end of the stick. Perhaps it's the
frequency of the grid (hence, the inertia of the spinning generators /
turbines / flywheels) that provides the "buffer" of energy needed to cope
with continually fluctuating supply and demand. Perhaps therefore, short
term frequency variance is "designed in".

It would be interesting if someone who knew more about this would comment.

Jon

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2003\11\17@114822 by David VanHorn

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>
>That's interesting, but suprising. Now, correct me if I'm wrong, but...
>
>Every generator set that contributes to the grid has to be running in
>perfect frequency and phase with the grid. Therefore, if immense loading on
>the grid would slow down the frequency, it must correspondingly slow down
>all of the connected generator sets and in turn, the turbines or engines
>that drive them. Which seems odd.

This was Oahu, Hawaii. We had a "grid" consisting of two generators.
Still, Oahu in the 70's was as civilized as it could get. :)

We had a large blackout and weeks of "rolling blackouts" after a cane fire shorted a transmission line, leading to an amusing industrial control incident that left us with one generator having a bent turbine shaft.

I think you need way more than two plants, to use a grid approach, so that any one plant can go offline without causing overloads elsewhere.

"you take the load".. "no YOU take it", "ok, I've got it", "Ouch overload, you take it"......  BANG.. Darkness falls.  Geckos chirp..

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2003\11\17@125245 by Hopkins

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Love your story, It may have been the voltage changing under load more than
the frequency, the frequency is usually pretty stable.

Another source of accurate frequency in most peoples houses is the TV set.
Just run a wire across the top of the TV set and you can pick up the scan
line frequency (depends what country you are in as to the actually
frequency), this frequency is ok for a calibration check.

If you know your TV set inside out then a more accurate frequency is the
colour burst frequency that is locked into the TV stations accurate
source.(WARNING don't go there if you don't know what you are doing)

:-) Roy

{Original Message removed}

2003\11\17@130114 by Jack Smith
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       Another source of accurate frequency in most peoples houses is the TV set.
       Just run a wire across the top of the TV set and you can pick up the scan
       line frequency (depends what country you are in as to the actually
       frequency), this frequency is ok for a calibration check.

       If you know your TV set inside out then a more accurate frequency is the
       colour burst frequency that is locked into the TV stations accurate
       source.(WARNING don't go there if you don't know what you are doing)

I've heard that the days when the color burst was locked to a network
Rubidium standard are long gone and that the local Broadcast station is
generating its own burst reference from a master crystal timebase. It's
still going to within a Hertz or two of standard, but not so close that you
can use it to calibrate your frequency counter timebase.

It's been a long time since I've set foot in a TV transmitter plant, so
perhaps someone knows the answer to this for sure.

In any event, the horizontal sweep frequency is certainly plenty accurate to
check the time base and horizontal linearity on an analog 'scope.

Jack

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2003\11\17@131527 by Mike Singer

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Jon,

it's not a bad idea to Google with

"Lissajous figure" Oscilloscope

This is "must read" topic for Oscilloscope users.

Get somewhere XTAL+oven based generator and
you'll measure AC frequency with your scope with
up to 0.00000001 precision.

Good Luck,

Mike.

> > > Sorry, that's me who got restricted to be not free to
> >> comment this kind of statements (perhaps
> > > due to I live in "wrong" i.e. "uncivilized" from
> > >someone's point of view part of the world).
> >
>
> I don't understand what you're saying ?!?

Lucky you are.

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2003\11\17@143622 by Jinx

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> The powerline frequency is only correct in the long term. (hours)
>
> I remember watching our school clocks visibly slow, when the
> local steel mill fired up.

As a seasoned clock-maker I can amen that. Line frequency
goes up and down during the day (slower at peak demand,
faster at low demand, eg overnight). Cycles per day is more
of a goal, not absolute frequency

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2003\11\17@143829 by Vincent Vega

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Mike Singer <m_singerEraseMEspam.....POLUOSTROV.NET> wrote:
Olin Lathrop wrote:
>> Any crystal oscillator will be far more accurate than any error
>> you can see on a scope.

>It's not that true, just feed X deflection channel of the scope
>with the sine from the temp-compensated sine generator and
>turn off synchronization.

How would he know?

>> ...In civilized parts of the world, the power line frequency is
>>controlled far more accurately than you can see on a scope...

>Sorry, that's me who got restricted to be not free to comment
>this kind of statements (perhaps due to I live in "wrong" i.e.
>"uncivilized" from someone's point of view part of the world).

Don't pay attention to comments that clearly show who the
civilized ones are. It's not the first time that kind of comments
appear on the list. Don't think all the people in the *civilized*
world are the same. You are from Ukraine Mike, aren't you?
Could you explain to me and some other fellows here, how
the *uncivilized* Ukraine designed and builded the biggest flying
aircraft on earth?
VV




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2003\11\17@172427 by James Cameron

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My father was protection design engineer for the largest (population)
grid in Australia.  It's therefore an area of interest for me.  He
retired around 1990, I think.

On Mon, Nov 17, 2003 at 04:30:39PM -0000, Hulatt, Jon wrote:
> Every generator set that contributes to the grid has to be running in
> perfect frequency and phase with the grid. Therefore, if immense loading on
> the grid would slow down the frequency, it must correspondingly slow down
> all of the connected generator sets and in turn, the turbines or engines
> that drive them. Which seems odd.

I thought having more load than generating capacity caused an increase in
frequency.  But I may have been confusing effect with control method.

> Furthermore, since "anyone" can contribute supply to the grid, and can only
> connect their generator set when it is perfectly in phase with the grid,
> then how on earth can someone realistically expect to get their generator in
> phase with a significantly changing frequency or phase?

They connect it with a device that can track the change and adjust their
generator set.  As you can imagine, if the set was connected with the
wave following the grid, the set would behave as a load.

I've heard stories of early phase detectors that could display zero for
180 degrees out of phase condition.  Generators leaping from turbine
housing.  But if I recall correctly, they were American stories.  ;-)

> Although, I could be getting the wrong end of the stick. Perhaps it's the
> frequency of the grid (hence, the inertia of the spinning generators /
> turbines / flywheels) that provides the "buffer" of energy needed to cope
> with continually fluctuating supply and demand. Perhaps therefore, short
> term frequency variance is "designed in".

In the control room (Carlingford) when I was there, was a frequency
counter with several digits after the decimal place, an atomic or radio
synchronised clock, and a 50Hz line frequency driven "domestic" clock,
showing hours, minutes and seconds.

Grid frequency was allowed to shift around within certain constraints,
subject to the load and generating capacity.  But once things were
stable, the main frequency control would be adjusted to bring the clock
back into alignment with real-time.  The aim was to provide very
accurate long term (many hours) average frequency.

One should be able to set a line frequency bedside alarm clock to the
second using the national radio's time signal, and then have it wake
with the theme introduction to the News at 6AM the next day.

Disclaimer: this was in the eighties, before the government sold the
operation as a business.  My memory needs refreshing.

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2003\11\17@192107 by John Ferrell

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What makes you think the scope will need calibration?

50 HZ line will be a coarse test.

Is there any other equipment available to you for test?
Do you know a Ham radio operator that might allow you to measure his
operating frequency? He will know where he is transmitting and no
connections are required.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
RemoveMEjohnferrellTakeThisOuTspamspamearthlink.net
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"


{Original Message removed}

2003\11\17@222709 by Dave Tweed

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Mike Singer <EraseMEm_singerspamspamspamBeGonePOLUOSTROV.NET> wrote:
> Olin Lathrop wrote:
> > Any crystal oscillator will be far more accurate than any error
> > you can see on a scope.
>
> It's not that true, just feed X deflection channel of the scope
> with the sine from the temp-compensated sine generator and
> turn off synchronization.

But then you're not using the scope's timebase, which is what the OP wanted
to calibrate.

-- Dave Tweed

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2003\11\18@012811 by Mike Singer

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Dave Tweed wrote:
> Mike Singer wrote:
> > Olin Lathrop wrote:
> > > Any crystal oscillator will be far more accurate than any error
> > > you can see on a scope.
> >
> > It's not that true, just feed X deflection channel of the scope
> > with the sine from the temp-compensated sine generator and
> > turn off synchronization.
>
> But then you're not using the scope's timebase, which is what the
> OP wanted to calibrate.


  I quoted Olin's statement:
"Any crystal oscillator will be far more accurate than any error you
can see on a scope."

And I replied to it, not to OP.
The idea was that having a wave generator one can measure
time-related values with the generator's precision , not scope's.

Getting simplest crystal based generator to a scope is not a big
deal even to a newbie. So the statement "Any crystal oscillator
will be far more accurate than any error you can see on a scope."
looked  a bit pessimistic, in my opinion.

Mike.

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2003\11\18@072730 by Olin Lathrop

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> The powerline frequency is only correct in the long term. (hours)

Even the instantaneous frequency is controlled plenty accurately enough to
calibrate a scope by.  Again, this assumes you are in a civilized part of
the world with a real power grid.  All bets are off when your village runs
on a diesel generator for 3 hours every evening from spare fuel swiped from
the cooperative so that the local party boss can watch his favorite TV
shows.


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2003\11\18@073145 by Olin Lathrop

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> Darkness falls.  Geckos chirp..

Geckos chirping?  I've heard of birds and insects chirping, but lizards?  Is
this one of those strange species that evolved on Hawaii?


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2003\11\18@074144 by Olin Lathrop

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> "Lissajous figure" Oscilloscope
>
> This is "must read" topic for Oscilloscope users.

Lissajous figures can be very useful to see if one signal is phase locked to
another, but they won't help you to calibrate your oscilliscope.

> Get somewhere XTAL+oven based generator and
> you'll measure AC frequency with your scope with
> up to 0.00000001 precision.

You're saying the temperature controlled crystal oscillators are good to
.01ppm (10ppb, parts per billion).  I thought the main point of an oven was
low drift due to temperature variations, but an oven doesn't guarantee
initial accuracy.  Crystals age over time, and I don't think it's possible
to produce them to such tolerance, even at a fixed temperature, in the first
place.  I could be wrong, but this seems like atomic clock territory.


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2003\11\18@080953 by Russell McMahon

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> > Darkness falls.  Geckos chirp..
>
> Geckos chirping?  I've heard of birds and insects chirping, but lizards?

Yep.
Chirping seems to be a standard description of what they do.
Would've fooled me too ;-)


       RM


______________

Geckos are a personal favorite of mine. They are unique among the reptiles
in that they are the most nocturnal, and they chirp.

   http://hotspotshawaii.com/nalostuff/May96/Geckos.html


The noise I have heard most often is the chirp, crackle, gurgle, clicking
(different people describe it different ways, ...

       http://www.thegeckospot.com/leocare2_5.html


Geckos, the small lizards that chirp through tropical nights,

   http://polypedal.berkeley.edu/Media_Tour/PlainDealer6_11_00


In "male" geckos the call is more dominant (Rösler, 1992). Susan G. Brown
and Susan Murphy-Walker (1996) describe it as a "multiple chirp call".

   http://home.t-online.de/home/0648491061-0001/en/lugubris_en.html

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2003\11\18@083241 by Hulatt, Jon

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> Olin Lathrop said...
>
> Crystals age over time,


LOL. so do most things :)

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2003\11\18@104059 by David VanHorn

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At 07:30 AM 11/18/2003 -0500, Olin Lathrop wrote:

>> Darkness falls.  Geckos chirp..
>
>Geckos chirping?  I've heard of birds and insects chirping, but lizards?  Is
>this one of those strange species that evolved on Hawaii?

Fools many tourists.. Birds don't chirp at night.  The Geckos are out hunting roaches.

Reminds me of the Hawaii Restaurant Rule:

If the roaches won't eat there, you shouldn't either..

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2003\11\18@144736 by Peter L. Peres

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>> and is there a fairly precise higher frequency waveform that I can use
>> in or from something else??
>
> Any crystal oscillator will be far more accurate than any error you can
> see on a scope.

A normal scope and a pair of eyes will let you see a 2% absolute error and
measure 5% (2% means 1/50th of the screen width at best, or +/-1mm for a
100mm on a side screen assuming all else is perfect). Both mains and a
crystal are far more accurate than this.

Peter

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2003\11\18@221941 by Mike Singer

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> > "Lissajous figure" Oscilloscope
> >
> > This is "must read" topic for Oscilloscope users.
>
> Lissajous figures can be very useful to see if one signal is phase
locked to
> another, but they won't help you to calibrate your oscilliscope.

You needn't calibrate new oscilloscope.
But with very cheap oscilloscope and few-bucks PIC-based
generator you can measure time-related values rather
precisely looking at Lissajous figures.
Cheap scopes are ssooo cheap, for they are intended to be used with such
external things.

> > Get somewhere XTAL+oven based generator and
> > you'll measure AC frequency with your scope with
> > up to 0.00000001 precision.
>
> You're saying the temperature controlled crystal oscillators are good
to
> .01ppm (10ppb, parts per billion).  I thought the main point of an
oven was
> low drift due to temperature variations, but an oven doesn't guarantee
> initial accuracy.  Crystals age over time, and I don't think it's
possible
> to produce them to such tolerance, even at a fixed temperature, in the
first
> place.  I could be wrong, but this seems like atomic clock territory.
>

I said "_UP TO_ xxx precision"
Just specs from one of my badly uncivilized devices manufactured in
ancient 1985.- true values, no doubt.

The reference frequency generator is set at a factory with 1E-8
precision.
Frequency relative error: 1E-7 for 30 days
Frequency relative error: 5E-7 for 12 months.

So for the civilized world brand new shiny devices with 10 times more
precision _MUST_  have been scattered here there and everywhere.

Mike.

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2003\11\19@123141 by M. Adam Davis

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It used to be that they had to be super accurate so they could switch
feeds with their networks without causing a rolling picture.  I imagine
now that they fix such problems with time base correctors, but I'll bet
they use a GPS timebase anyway, so they know /when/ their parent is
sending the next commercial and they can catch and juggle and send
things without missing frames.

-Adam

Jack Smith wrote:

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2003\11\20@083032 by Jack Smith

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The joint US/Canada Interim Report on the August 14th Blackout is available
at https://reports.energy.gov/814BlackoutReport.pdf.

The Report has a graphic showing the range of frequency excursion for the
North American power grid, with "normal" frequency excursions in the range
60.01Hz - 59.99Hz, and with "time correction" adjustments over the range
60.02Hz - 59.98Hz.

Over frequency trip is not until around 61.5Hz and under frequency trip at
58.5Hz.



Jack

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