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

Dave Martindale dave.martindale at gmail.com
Tue Apr 15 12:41:46 EDT 2014

Here is a discussion forum page that shows a commercial quartz watch 
timing machine in use:

The machine obviously measures the time of each second "tick", either 
electrically or acoustically, because it can tell you the instantaneous 
rate over one second based on the time between ticks. In the example 
shown, the crystal is fast by 4.18 seconds/day (48 PPM) based on the 
period between most ticks, but every 60th tick has a longer period due 
to inhibition (oscillator pulse dropping), and the net rate measured 
over 60 seconds is 0.32 seconds/day (3.7 PPM).

There is a bunch of additional information about the motor drive pulses 
too.  The article explains what it means in some detail.

It seems to me that calculating the rate information should require 
nothing more than capturing the leading edge of each motor pulse and 
time stamping it, at a rate of 1 data point per second.  The motor 
information requires capturing several pulses (at a rate of a few kHz 
max.) every second.

- Dave

On 15/04/2014 09:52, Tom Van Baak wrote:
>> Some research has shown that there is an comparable instrument for ANALOG
>> quarz watches. As far as I understand it does not try to detect the quarz
>> frequency but detects magnetic pulses from the step motors that move the
>> hands of the watch.
>> Has anyone of you ever tried to do this in a time nuts laboratory?
> Ulrich,
> Yes, this works well, for both those with seconds hands (one magnetic pulse per second) and those with only minute/hour hands (one or two steps per minute). A large coil of wire is all you need. Have a look at the watch timing tools and sensors at http://www.bmumford.com/microset.html or http://www.bmumford.com/mset/modelwatch1.html
> Here's an example using a magnetic sensor: http://leapsecond.com/pages/Junghans/
> /tvb
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