Wikipedia: Rotary dial

Showing revision 6

The rotary dial is a device mounted on or in a telephone or switchboard that is designed to send interrupted electrical pulses to a remote site equivilant to the number dialed. The dial is circular, about three inches in diameter, with 10 fingerholes cut through the outer perimeter. The dial is mounted via a shaft extending from inside the phone or mounting and sits approximately 1/4 inch above a faceplate. The faceplate is set so that through each fingerhole letters and numbers printed on the faceplate may be seen. Traditional dials have thier fingerholes labeled as 1, 2 ABC, 3 DEF, 4 GHI, 5 JKL, 6 MNO, 7 PRS, 8 TUV, 9 WXY and 0 Operator. The 1 is normally set at what would be 2 o'clock and then the numbers progress upward counterclockwise, with the 0 being at about 5 o'clock. A curved device called a fingerstop sits above the dial at the 4 o'clock position. If a user wants to dial a 6, he or she would put his finger in the 6 fingerhole and rotate the dial clockwise until he reaches the fingerstop. He will then pull out his finger and a spring in the dial will return it slowly to the normal position. As the dial returns, electical contacts wired through the mechanism underneath will open and close 6 times, thus sending 6 pulses to the receiving end.