Rotary dial

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The rotary dial is a device mounted on or in a telephone or switchboard that is designed to send electrical pulses, known as pulse dialing, corresponding to the number dialed. The early form of the rotary dial used lugs on a finger plate instead of holes. A patent was filed on August 20, 1896 by employees of Almon Strowger, namely, A. E. Keith and the brothers John and Charles Erickson. The Patent No. 597,062 was granted on January 11, 1898.

The modern version of the rotary dial with holes was first introduced in 1904 but only entered service in the Bell System in 1919. The rotary dial was gradually supplanted by Touch Tone dialing, introduced at the 1962 World's Fair, which uses a keypad instead of a dial. Some telephone systems in the US no longer recognize rotary dialing by default, but will only support push-button phones instead, in which case the rotary dialing system would have to be ordered from the telephone company as a special feature, to support older customer equipment. However most actually do accept dial phoning without fail.

In telephony, the word dialing describes the process of placing a telephone call, or more specifically of entering the number to be called into the telephone system.



From as early as 1836, there were various suggestions and inventions of dials for sending telegraph signals. After the first commercial telephone exchange was installed in 1878, the need for an automated, user-controlled method of directing a telephone call became apparent. The first telephone dial patent was jointly issued to Connolly and McTighe in 1879. There were numerous competing inventions, and 26 patents of dials, push-buttons, and similar mechanisms for signalling which telephone subscriber was wanted by a caller were issued prior to 1891. Most inventions involved highly complex, and expensive, mechanisms and required the user to perform complex manipulations.

The first commercial installation of a Telephone Dial accompanied the first commercial installation of a 99 line automatic telephone exchange in La Porte, Indiana in 1892, which was based on the 1891 Strowger patent designs. The original dial designs were rather cumbersome and development continued during the 1890s and early 1900s hand in hand with the switching technology. In the 1950s, invention of plastics saw the dial itself change from metal disk to a plastic ring.

In the early 1960s Bell Telephone Laboratories researched various key pad layouts to replace the telephone dial, for electronic telephone equipment. Human tests were conducted to finalize the position of the keys to limit errors and increase dialing speed. The first touch tone telephones were a big hit at their release and were highly accepted by consumers. Researchers rearranged the dial numbers in a wide range of combinations from mimicking a telephone dial to the now familiar 4 row by 3 column keypad. They found the 4x3 keypad to be the fastest and most error free arrangement to operate. However, because the American telephone dial had the 0 next to the 9, they tested the arrangement with a 1 at the top and 0 at the bottom, below the 8 key. They also tested an arrangement with the 0 below the 2 and having 9 at the top, as appeared on adding machines at that time and now appears on computer and calculator keyboards, but that arrangement was more error prone as few people were familiar with adding machines at that time. Because of this research, phone key pad numbering is reversed when compared to today's calculator and computer keyboards. However, the keypads of most cash machines usually have the same numbering as phone key pads.

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