Mechanical counter
Mechanical counters are digital counters built using mechanical components. Long before electronics became common, mechanical devices were used to count events. They typically consist of a series of disks mounted on an axle, with the digits zero through nine marked on their edge. The right most disk moves one increment with each event. Each disk except the left-most has a protrusion that, after the completion of one revolution, moves the next disk to the left one increment. Such counters were used as odometers for bicycles and cars and in tape recorders and fuel dispensers and to control manufacturing processes. One of the largest manufacturers was the Veeder-Root company, and their name was often used for this type of counter. Mechanical counters can be made into electromechanical counters, that count electrical impulses, by adding a small solenoid. (Wikipedia).
