There is no rule as to the weight of a clock pendulum; it is regulated, according to the quality of clock. The best clocks carry the heaviest pendulums. Weight does not affect the time of vibration ; that depends solely on the length. There is no formula for determining the friction or resistance to the air of a pendulum. To find the length of a pendulum for any given clock, first find the number of vibrations it is required to make in one minute, and then find the length of a pendulum making that number either from a table or by calculation. To find the required number of vibrations per minute, multiply together the numbers of the teeth in the centre wheel, third wheel, and scape wheel. Divide this by the numbers of the third pinion and 'scape pinion and 30. Thus, suppose the centre wheel is 61, third wheel 60, pinion 8, 'scape wheel 30, pinion 8, then (64x60x30)/8x8x30=60=number of vibrations per minute.

To find the length of the pendulum miking this number of vibrations per minute, divide 375.4 by the number and square the result. Thus 375.4/60= 6.26; this squared = 39.18, which is approximately the length of the seconds pendulum in England.