corresponding to the digits 1-9, and 0 (which sends 10 pulses). This equipment originally consisted of two telegraph keys engaged by knife switches, and evolved into the rotary dial telephone.

The central office switching equipment has a two-motion stepping switch. A contact arm is moved up to select one of ten rows of contacts, and then rotated clockwise to select one of ten contacts in that row, a total of 100 choices. The stepping motion is controlled by the