The comptometer was the first commercially successful key-driven mechanical calculator, patented in the United States 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 as many fingers as required, making them sometimes faster to use than electronic calculators.

Comptometer

Although the comptometer was primarily an adding machine, it could also do subtractions, multiplication and division. Its keyboard consisted of eight or more columns of nine keys each. Special comptometers with varying key arrays were produced for a variety of special purposes, including calculating currency exchanges, times and Imperial weights. The name comptometer was formerly in wide use as a generic name for this class of calculating machine.

Dorr Eugene Felt

Dorr Felt began his work on comptometer in 1882 and started building first prototype during the American Thanksgiving holidays of 1884. Because of his limited amount of money, he used a macaroni box for the outside box, and skewers, staples and rubber bands for the mechanism inside. It was finished soon after New Years Day, 1885. This prototype, called the macaroni box, is in the Smithsonian Institution in Washington, D.C., United States.
Shortly after, Robert Tarrant, the owner of a Chicago workshop, gave Mr. Felt a salary of $6 a week, a bench to work on and what would add up to $5,000 to build his first practical machine which he finished in the autumn of 1886.
By September 1887, eight production machines had been built.

Patented

The original comptometer design was patented by Felt, on July 19, 1887 and on October 11, 1887.
Two years later, on June 11, 1889, he was granted a patent for the Comptograph.