On this date in 1887, Dorr Felt invented what became known as the comptometer, a mechanical or electro-mechanical adding machine. The comptometer was the first adding device to be driven solely by the action of pressing keys. Although the comptometer was designed primarily for adding, it could also subtract, multiply and divide simply by pressing keys. 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remained in use in limited numbers into the 1990s, but with the exception of a handful of machines, have now all been superseded by computer software.
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