On rotary dial phones smaller numbers, such as 2, are dialed more rapidly than longer numbers, such as 9 (because the dial turns much further with a 9). In 1947, area codes were introduced in the United States, so as to facilitate direct distance dialing first by operators, then by subscribers. In the original system in use until 1995, the first digit of the area code could not be a one or a zero, but the second number had to be a one or zero. This allowed mechanical switching equipment in the central offices to distinguish local from "long distance" calls, since one and zero have no associated letters that could spell out telephone exchange names.