Stepping switch

In electrical controls, a stepping switch (or uniselector) is an electro-mechanical device used, most priminently, in early automatic telephone exchanges to route calls. Such switches were also used in a series of Japanese cypher machines during World War 2: Red, Coral, Jade, PURPLE. (The names are those used US cryptgraphers and have nothing to do with any aspect of the cyphers -- they are the colors of binders used to hold information about the cyphers as they were worked on.)

External Link

• Explanation of the way a stepping switch works