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A Comptometer is a type of mechanical (or electro-mechanical) adding machine. The comptometer was the first adding device to be driven solely by the action of pressing keys, which are arranged in an array of vertical and horizontal columns.

"Comptometer" is a trade name of the Felt and Tarrant Manufacturing Company of Chicago (later the Comptometer Corporation, and then Victor Comptometer Corporation), and after 1961 was licensed to Sumlock-Comptometer of Great Britain. It is widely used as a generic name for the class of device.

Although the comptometer was designed primarily for adding, it could also do division, multiplication and subtraction. Special comptometers with varying key arrays (with from 30 to well over 100 keys) were produced for a variety of purposes, including calculating currencies, time and Imperial measures of weight.

In the hands of a skilled operator, comptometers can add numbers very rapidly, since all the digits of a number can be entered simultaneously using as many fingers as required, making them much faster to use than electronic calculators. Consequently, in specialist applications they remained in use in limited numbers into the 1990s, but with the exception of a handful of machines, have now all been superseded by computer software.

Source: Wikipedia - Comptometer

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