It seems that the more accurate a clock is, the higher the frequency of the oscillator.

Is this assumption right? Is this due to a general physical principle?

I look after a pendulum clock at the University of Cambridge which I hope will achieve an accuracy of less than 1 second of error per year (www.trin.cam.ac.uk/clock). It has a temperature-compensated pendulum, but is sensitive to air pressure variation.

If the mean global temperature was to rise by, say, 4 °C, would there be any change to mean air pressure at sea level? Put simply, would global warming cause the clock to speed up or slow down?

Hugh Hunt, Keeper of the Clock, Trinity College, University of Cambridge, UK

Photographs of the clock mechanism in the tower of the UK's Houses of Parliament (Big Ben) show coins on a tray attached to the pendulum being used to tune the oscillation period. Since we all know that mass doesn't affect the period of a pendulum, why is this done?

Tony Richardson, Ironbridge, Shropshire, UK