"When it is required to ascertain the length of pendulum for a clock, first calculate the number of beats per minute that the pendulum is required to make. To do this, multiply together the number of teeth in the centre wheel (that carries the minute hand), the third wheel, and the 'scape wheel. Also multiply together the number of leaves in the third-wheel pinion and the 'scape-wheel pinion. Divide the product of the wheels by the product of the pinions and multiply the result by 2. This gives the number of beats per hour. Divide it by 60, and this will give the number per minute. The length of a pendulum to beat 60 per minute (the seconds pendulum) may for convenience be taken as 40 in. The length of a pendulum to beat any other number can be found from it by simple proportion, remembering that the length will be inversely as the square of the number of vibrations. Thus, for a pendulum to beat 103 per minute: as 1003:60s:: ±0 in. to 14.4 in.