The Panel telephone switch was an early type of automatic telephone exchange, first put into service in the 1920s. While the Strowger (step-by-step) switch moves synchronously with the dial pulses that come from the telephone dial, the Panel switch allows one digit of dial-ahead. Since the dial pulses come at a fixed rate, a single-digit dialahead can be guaranteed by the design of the Panel switch. central office = Exchange building in the U.S. telephone exchange = Exchange building in the UK, and is also the UK name for a telephone switch, and also has a technical meaning in U.S. telecoms telephone switch is the U.S. term, but is in increasing use in technical UK... Pulse dialing or loop disconnect dialing, also called Rotary or Decadic dialling in the United Kingdom (because up to 10 pulses are sent), is pulsing in which a direct-current pulse train is produced by interrupting a steady signal according to a fixed or formatted code for each digit and... This article needs to be cleaned up to conform to a higher standard of quality. ...

A good description of the Panel switch can be found in the Survey of Telephone Switching.