1) Mechanical calculator 
The comptometer was the first commercially successful key-driven mechanical calculator, patented in the USA by Dorr E. Felt in 1887. A key-driven calculator is extremely fast because each key adds or subtracts its value to the accumulator as soon as it is pressed and a skilled operator can enter all of the digits of a number simultaneously, using ...
• (n.) A calculating machine; an arithmometer.
Comp·tom'e·ter noun [ See Count ; -meter .] A calculating machine; an arithmometer.