Editing Pulse dialing (section)

==Rotary dial==
The first rotary dials worked by creating current interruptions on two separate direct current circuits (three-wire system) to actuate stepping motors in a vertical and horizontal (rotational) switch arrangement. Operating the dial error-free required smooth rotary motion of the finger wheel by the user, but was found as too unreliable. Later dials after c. 1907 produced just a single pulse train on a 2-wire circuit as the user rotated the dial to the finger stop starting at a different position for each digit transmitted. This mechanism was refined to include a recoil spring and a [[centrifugal governor]] to control the recoil speed. The user selected a digit to be dialed by inserting a finger into the corresponding hole and rotated the dial to the finger stop. When released from this position, the dial pulsing contacts were opened and closed repeatedly, thus interrupting the loop current in a pattern on the return to the home position. The exchange switch decoded the pattern for each digit thus transmitted by stepping relays or by accumulation in digit registers.