Revolution counter, inscribed with numbers

Revolution Counter by engineer Richard Roberts, 1862

This counter indicates by the use of two concentric revolving dials geared together by an epicyclic train. The dials are on a central fixed stud, which also carries a double-ended pointer. The larger dial has a toothed edge and is driven by a worm from the shaft whose revolutions are to be counted; the ratio of the gearing is 1 : 100, so the dial counts up to 100 rev. The dial carries at the back a pin, upon which runs a long pinion gearing into a spur wheel of thirty-nine teeth fixed to the stud, and also into a wheel of forty teeth secured to the back of the inner dial. By this means the inner dial, which reads up to 4,000, is rotated at 1-40th of the speed of the outer one.