In article ,
Jeff Liebermann wrote:


Accutron watches

-- snippage --


A more interesting problem was mechanical vibrations in the 360Hz
range. (the frequency of the tuning fork). When my watch was working,
it would tend to run quite fast if I was working near big synchronous
or induction motors driven by 60Hz such as in my fathers clothing
factory. It was not unusual to gain about a minute, after spending an
hour pushing cloth through an industrial sewing machine (with my hands
on the table).

I used mine for sports car rallies, and needed to synch it to WWV fairly
often (weekend rallies), but it was damn hard to set to the nearest
second even though I had the jeweler install the "hack" feature. I
learned to adjust it to run just slow enough so that accidental knocks
and so on would never put it ahead of time during the week. Then, simply
by giving it a good "thump" on the edge, I could overdrive the fork
briefly (it would do a three-tooth push on the driven gear instead of
the usual two), which would make it gain a good fraction of a second. A
few of those would get the thing spot on.

I suspect (guess) that vibration was also the problem
in airplanes, not thin air.

Bulova said it was air density.

Temperature is of course a problem:
http://bmumford.com/mset/tech/accutron/index.html

As well as every other momentum-transfer effect that plagues tuning
forks. Interestingly, they also affect those 32,768 Hz. crystals because
they are physically shaped like tuning forks (that's the only
oscillatory mode that can run that slowly in such a small piece of
quartz).

John Harrison's marine chronometer, developed for the British navy in
the mid-1700's, was good for about a minute a month, which was
considered the lowest accuracy usable for navigation. The Accutron was
the first "commercial" watch to have the same accuracy.

Isaac