Wiktionary
n. An electromechanical device which connects an input to one of a number of outputs according to how many electrical pulses it has received on its input.
Wikipedia
In electrical controls, a stepping switch or uniselector (UK), also known as a stepping relay, is an electromechanical device which allows an input connection to be connected to one of a number of possible output connections, under the control of a series of electrical pulses.
It can step on one axis (called a uniselector), or on two axes (a Strowger switch). Stepping switches were invented by Almon Brown Strowger in 1888. The major use for these devices was in early automatic telephone exchanges (commonly called Strowger or step-by-step exchanges or steppers) to route telephone calls. Later, they were often used in such equipment as industrial control systems.
Stepping switches were used in Japanese cypher machines during World War 2, known to the Americans as CORAL, JADE, and PURPLE. World war 2 code breakers at Bletchley Park employed motor uniselectors in Colossus and Tunny to decrypt German ciphers.1
Usage examples of "stepping switch".
Vexed by the fact that the local operator in his town referred the bereaved to a competing undertaker, he had invented the stepping switch, which enabled people to reach their own phone destinations merely by turning a rotary dial.