[time-nuts] Adjusting accuracy of a Casio G-Shock watch

Jim Palfreyman jim77742 at gmail.com
Wed Dec 15 22:53:23 UTC 2010


Hi Brooke,

I've adjusted the watch as best I can within the limitations of the trimmer.
The waveform was drifting 10 microseconds (slow) in about 20 seconds and so
this should come out to 1 second in 23 days.

I have now set the watch accurately and will follow it's progress. I plan to
see how long it takes to be a second out and then re-open the cover and
re-check the wave form.

>From that I should be able to work out the relationship between the measured
frequency and actual watch accuracy.

Watch (*cough cough*) this space.

:-)

Jim

P.S. I'm so looking forward to being able to have a genuine atomic watch on
my wrist. Surely it can't be too far away...


On 16 December 2010 06:03, Brooke Clarke <brooke at pacific.net> wrote:

> Hi Jim:
>
> It may not be a good idea to adjust the watch so that the frequency is spot
> on at the time the adjustment is made.
> A better idea may be to wear the watch for a week and note the fractional
> time error then adjust the frequency so the offset matches the error.
>
> Have Fun,
>
> Brooke Clarke
> http://www.PRC68.com
>
>
> Jim Palfreyman wrote:
>
>> Fellow time-nuts.
>>
>> Over in another part of the internet is a group of people who love their
>> Casio G-Shock watches. These digital watches have been around for decades
>> and are built very well.
>>
>> The one I own is an "atomic" and solar model (i.e. no battery
>> replacement).
>> However being in Tasmania, I cannot receive the low frequency time
>> signals.
>> When I first received the watch it's accuracy was excellent. Under 10
>> seconds a year. I even posted on here about it. Since then though it has
>> drifted somewhat.
>>
>> After a ton of internet searching on how to open the case and how to
>> adjust
>> these watches (this is non trivial as the models are all very different
>> and
>> no instructions existed for this model - the GW-810D) I have finally
>> cracked
>> it.
>>
>> Interestingly, the module has a pad that gives off a stepped square wave
>> at
>> 32768/48 Hz. So with well calibrated equipment (which we all have of
>> course)
>> it is trivial to adjust the trimmer to put the watch back to decent
>> accuracy. Using the smallest adjustment of the trimmer that I could muster
>> I
>> could get it down to about 0.5 in 10^6 or 1 second in around 20 days. Not
>> as
>> good as when I got it - but I was probably just lucky.
>>
>> Over in mygshock.com they struggle with this sort of timing stuff -
>> whereas
>> my big deal was opening the case!
>>
>> Just posting in this in case anyone here is interesting in adjusting their
>> G-Shock.
>>
>> Jim
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>>
>
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