Comptometer 1. Model

Swing lever machine

ca. 1890

Dorr E. Felt (1862 - 1930) constructed a calculating machine in the USA in the 1880s, which was manufactured under the name Comptometer for about 80 years. He and his competitor William S. Burroughs are among the most successful designers and manufacturers of mechanical adding machines. After the production of the first experimental model ("Macaroni Box", FDM 6282), he was granted US Patent No. 371496 dated 11 October 1887, and Felt produced the first eight machines in 1886/87, which were presented in Washington in September 1887. With his partner Robert Tarrant, Felt founded the company Felt & Tarrant on 25 January 1889 for the manufacture and sale of the Comptometer. In the early 1890s, production of the first commercial comptometer began, recognisable by its wooden case, which was replaced in 1903 by the Model A with a metal case. Altogether about 6500 copies of the first model were built, as it was found out from lists of serial numbers. About 100 of these are still in private and public collections. The machines are driven by pressing a button, a crank is not necessary. The key shafts press on the switching lever, which, depending on the position of the key, is pressed downwards accordingly and then, when it swings back into the rest position, makes the numerical entry in the result mechanism. The tens transfer is based on a very special technical solution, which is carried out with the help of a worm step disc. Here is one of the very early examples, where the deletion is controlled by a removable key.