The comptometer was the first commercially successful key-driven mechanical calculator, patented in the United States by Dorr Felt in 1887. It was a key-driven calculator that was extremely fast because each key adds or subtracts its value to the accumulator as soon as it is pressed.
The comptometer was the first commercially successful key-driven mechanical calculator, patented in the United States by Dorr Felt in 1887. It was a key-driven calculator that was extremely fast because each key adds or subtracts its value to the accumulator as soon as it is pressed.
Source: Wikipedia "Comptometer" · CC BY-SA 4.0
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