[time-nuts] Measuring the accurcy of a wrist watch

Al Wolfe alw.k9si at gmail.com
Thu Apr 17 13:25:37 EDT 2014

    Thank you for your response. I don't think I could improve on the 
accuracy of this old watch much by trying to "regulate" it. I was more 
curious to see if there was any way to determine what was going on in side 
it with out actually opening it.

    The buttons on the side have long ceased to function their being clogged 
with sweat and other detritus. Now even with it opened up the little switch 
contacts inside seem to do nothing. It is set to DST so is useful most of 
the year here. I tried to set it to standard time last Fall but gave up. It 
was thirteen seconds fast then and now down to eleven seconds fast. I think 
I will not mess with it any more till the battery dies. I have several other 
toys to play with if I really need to know what time it is.


>>    I have a Timex watch that's probably seven or eight years old. It has 
>> an
>> LCD readout. The buttons haven't worked in years. It looses about one 
>> second
>> every three or four months. I have to take out the four microscopic 
>> screws
>> in the back to get into it to set it. The only reason I hang onto it is 
>> that
>> is the most accurate watch I've ever owned.
>>    Is there some way to detect its internal frequency inductively? In the
>> past I have used old relay coils as inductive pickups with success, but
>> never with a watch.
>> Al
> Hang on to that one; that's an unusually accurate watch.
> I have been unsuccessful at picking up timing signals from a LCD watch. I 
> did try a webcam once but the timing resolution of an LCD display is 
> rather poor, in the 10 to 100 ms millisecond range. If you look a LCD 
> closely you'll notice how slowly the contrast transitions occur. The 
> acoustic, mechanical, electrical, and magnetic methods offer greater 
> resolution, but none of those work on LCD watches.
> I wonder if a fine (sub-mm) optical sensor that tracks contrast changes in 
> a single segment would work. On a 7-segment display, the 'd' segment is 
> the best one to aim for since it changes 8 times every 10 seconds.
> If you open it you may see a number of traces from the IC to the LCD with 
> pulse rates tied to the main oscillator. The problem here is that by 
> opening the case and measuring these extremely low current signals you 
> likely introduce a frequency offset.
> When you say "set it" do you mean adjust the time or adjust the rate? One 
> idea to reset the time by a few seconds without opening it: raise or lower 
> the temperature by many tens of degrees for some number of hours or days.
> /tvb

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