[time-nuts] Quartz assisted pendulum clock.

[Hal Murray]

> Of course, for the utmost accuracy one would run any crystal
> oscillator  24/7 and not want any breaks in power. But I think the
> mechanical play  on the hands is more significant than errors in the
> crystal oscillator -  at least on my clock.

Depends on the temperature and the crystal.

The 32 KHz crystal in my PC swings by about 2 PPM per 10 degrees F.
My junk room where the computer is located swings by about 10 F over a day.
  http://www.megapathdsl.net/~hmurray/ntp/drift.gif
(Or at least did when I made that graph.)

I think that's a cheap watch crystal, but I assume somebody gave some thought 
to temperature stability.  It might be optimized for wrist temp rather than 
room temp.


> I believe Big-Ben in the UK can be corrected by adding pennies to it,
> so  providing an upwards force. That is what I am told, but I must
> admit it  seems a bit unlikely. Perhaps possible if there are a lot of
> pennies  there. Apparently this is done, as it allows corrections
> without  stopping the clock. 

I've heard that story before, probably from Dave Mills.

A quick google easily finds it.

This URL
  http://news.bbc.co.uk/1/hi/uk/1501943.stm
says a penny is good for 2/5 second per day, ~5 PPM.

If we knew how big a penny was and assume the density of the pendulum is the 
same as a penny and assume something about the shape of the pendulum, say 
cylinder with dia equal to height, then we should be able to compute the size 
of the pendulum.




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