Shaft A is driven by the shaft whose speed is to be measured and, through friction clutch 2, shaft A rotates cone 1. Cone 1 is connected by gearing to centrifugal governor 3 which maintains constant speed of the cone. Shaft B is driven from shaft A through bevel gears 4 and 5, and has a helical thread along which friction wheel 6 can be traversed. The peripheral speed of wheel 6 at its point of contact with cone 1 is equal to the peripheral speed of the cone. If the angular velocities of wheel 6 and cone 1 differ, wheel 6 will be moved along shaft B until they are the same. The movement of friction wheel 6 is transmitted by fork 7 to gear rack 8 which meshes with pinion 9 of hand 10. The hand indicates the speed of shaft A and of the shaft whose speed is being measured.
$3443$CF,M$