Adding Machines
Full-Keyboard – Hill to Felt & Tarrant

An image displaying several adding machines from the Division of Medicine and Science.

In the mid-19th century, the Unitarian minister, mathematician and inventor Thomas Hill envisioned an adding machine that would have a column of keys for each digit entered. Hill took out a U.S. Patent for the device, but it never became a practical product.

Almost thirty years later, Chicago machinist Dorr E. Felt (1862-1930) decided to design an improved adding machine for accountants. Like Victor Schilt, he was interested in adding machines with keys, but he wanted to add larger numbers and to add them quickly. To do this, he devised a machine with several columns of keys. In each column, the keys were numbered from 1 to 9. The column as a whole represented one digit of a number. Felt first made a crude model using a macaroni box from a local grocer, with meat skewers for key stems and rubber bands for screws. He built several prototypes of the machine, and named it the Comptometer. Felt also soon built a printing version of the machine, which he called the Comptograph. It never sold widely.

On Felt’s Comptometer, pushing a key not only set up a digit, but entered it into the mechanism. Felt carefully cultivated customers, and won the financial support of Robert Tarrant as well as orders from government offices, businesses, and scientific observatories. Felt & Tarrant Manufacturing Company sent its products overseas as well as across the country. It built special Comptometers for adding fractions and non-decimal currency, and steadily improved, but did not radically alter, the product. Felt & Tarrant used some of its profits to acquire adding machines of historic interest.

Felt died in 1930. After considerable debate, descendents of Felt and Tarrant decided to take the firm public in 1946, taking the name Comptometer Corporation. The postwar years proved difficult, especially for foreign sales. In 1961, the firm merged with the Victor Adding Machine Company of Chicago to form Victor Comptometer Corporation. The products of this company looked quite different from those of Felt & Tarrant, as they were ten-key, printing machines. Not long thereafter, Victor Comptometer donated Felt’s collection of historically important machines to the Smithsonian.