[time-nuts] Pendulums & Atomic Clocks & Gravity

[Mike S]

At 01:17 PM 5/26/2007, Brooke Clarke wrote...
>Just starting to adjust the bob on a pendulum clock... Tom has pointed 
>out that the stability limit on pendulum clocks is in the area of 1E-7 
>because of the complex effect of the Sun and Moon on the value of "g".

I'd think it would be significantly less than that for real clocks due 
to fluctuations in air density caused by barometric pressure (affects 
friction unless in a vacuum) and in pendulum length due to temperature 
variation (the linear coefficient of thermal expansion is in the 
1.5e-5/degree C range for most metals, and 5e-6 for wood).