[time-nuts] Line Frequency

[Chuck Harris]

There were lots of those watch timing devices back in the days
of yor.

I have a Swiss machine called a Vibrograf B100.  It is a vacuum
tube instrument with a very simple printer that consists of a
rotating drum with a spiral wire wrapped around it that is hit
by a bar once for every tick of the watch's escapement.  There is
a typewriter ribbon and a paper tape between the bar and the drum,
and a dot is made on the tape for every tick.  The drum runs in
synchronism with the ideal rate for the watch's escapement. It
makes a nice tape of the phase data.

It doesn't really matter how accurate the xtal is, as that is not
how the instrument is generally used.  The xtal gets the watch
close to proper rate, and then the watch is set and given to the
customer.  The customer wears the watch for 1 week, and then brings
it back to the shop.  The watchmaker observes the time on the watch
and compares it to his standard clock, and calculates the error rate
for the watch as worn by the customer.

On the Vibrograf machine is a dial that allows you to set an offset
correction, and displays the slope the ticks on the tape should show
for that offset.

The watchmaker puts the watch back on his Vibrograf machine, and
observes the slope on the tape, and adjusts the offset dial to match
the slope.  He reads out the current error relative to the Vibrograf's
xtal, and then then factors in the error observed on the watch
relative to "real" time, and sets the offset dial to compensate for
the personal error rate.  He then adjusts the balance so that the
watch exactly matches the slope depicted by that corrected error rate.

The customer then takes the watch away, and is amazed that the watch
is always within a couple of seconds of reality.

-Chuck Harris

Tim Shoppa wrote:
>>   IIRC some watch or clock company had a patent on calibrating a
> wristwatch crystal against AC hum. I read it once but can't find it now.
> Can you hunt for it?
>
> Tom - when I was a kid in the 1970's, before digital watches, the local
> jeweler had device with a table on which a watch or clock could be placed,
> the table must've been a microphone, and it had a pen recorder. It produced
> a chart that looks like the "phase data" charts on yours and other
> websites; the jeweler adjusted the clock so the recorded line had no slope.
> It had a selector for several common watch/clock gear ratios (don't think
> it did the tuning fork watches like the Accutron; I think there was a
> similar but different device for checking the tuning fork Accutrons, my dad
> was enough of a clock nut that he actually had a tuning fork Accutron, and
> he is a NAWCC member still!). Over the course of an hour the adjustment
> could be fine trimmed to the point where we knew the movement was good to a
> few minutes a month. Don't know if it was locked to mains frequency or had
> a crystal. Do you know what this was called?
>
> Tim N3QE
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