The Felt's comptometer was the first calculator constructed that allowed operands to be entered by pressing keys rather than requiring the operator of previous calculators to turn a series of dials to input the operand values. (Operands are number values; the comptometer accepted operands of up to ten digits.) Upon its introduction, the machine was called "the epitome of convenience" because a user simply "tapped" in the numbers on a typewriter-like keyboard, and the machine made the necessary calculations with the use of springs that drove the mechanism. The 1886 invention by machine designer Dorr Eugene Felt (1862-1930) of Chicago, Illinois was accomplished due to an earlier Felt invention, a "carry" mechanism that allowed keys to quickly return to their rest-state after being pressed. The first rough draft of the Comptometer was finished near the end of 1884, and consisted mostly of rubber bands, meat skewers, and a macaroni box. The first working version, made from metal, was finished in around 1886, and limited production began in 1887. Over the next several years Felt continued his partnership with Robert Tarrant to manufacture and refine the Comptometer. Later, Felt added a built-in printer for the Comptometer that automatically recorded the inputs and outputs.

Herman Hollerith invented the Electric Tabulating System at about the same time as Felt invented his Comptometer. While Hollerith's tabulator was originally called a "sorter-counter" and the Comptometer was a machine to "add up" values, both solved the routine, often tedious, problem of record keeping. Hollerith's tabulator and Felt's comptometer were machines that provided a fast, efficient, and reliable method for counting and totaling. Over the next 50 years the Tabulator and the Comptometer were rivals for the data processing market.

The Comptometer is a historically significant machine, even called a pivotal breakthrough at its time of invention, because it was the first successful multiple-order, key-driven calculator. Although Felt's new carrying mechanism was complex, it provided the high-speed requirement needed by the Comptometer. The Comptometer could add faster than an accountant could manually perform addition, which was the key to its success.