Rotary Dial

A rotary dial is a component of a telephone or telephone switchboard that carries out a signaling method known as pulse dialing, transmitting a destination telephone number to a telephone exchange as a series of individual digits. On a rotary dial, the digits are arranged in a circle with one finger hole for each digit; dialing a digit means rotating the finger wheel clockwise against spring tension to a mechanical stop, then releasing it so the wheel returns to its resting position at a speed set by a governor, interrupting the telephone line's direct current the number of times that corresponds to that digit. The first patent for an automatic telephone exchange was granted to Almon Brown Strowger in 1892, but the rotary dial with a finger wheel was not introduced until around 1907, and from the 1960s onward it was gradually replaced by push-button telephones using Touch-Tone dialing.