Comptometer

The Comptometer, invented in 1887 by Dorr Felt, was the first mechanical calculating machine, which was operated only by pressing keys. Each decimal place had a series of nine keys with the values ​​1 to 9 Although the Comptometer was designed mainly for addition and subtraction, he dominated the other basic arithmetic. All decimals of the numbers to be processed could be entered simultaneously or sequentially. The simultaneous input the numbers were compared to the sequential input at today's pocket calculators, to be entered more quickly.

There was Comptometer for special applications such as the currency bill; these versions could have between 30 and 100 keys.

In some areas Comptometer were still up in the 1990s in use.