A post from Shady Characters

Shady Char­ac­ters advent calendar 2023: the Comptometer

This is the sixth in a series of twelve posts on 2023 Advent calendar. Start at PART 1, continue to PART 7 or view ALL POSTS in the series.

This monster, this typewriter-adjacent behemoth, is a Comptometer. It was the brainchild of a Wisconsinite named Dorr E. Felt, and it was born in a macaroni box.1

A Comptometer dating to around 1887.
A Comptometer dating to around 1887. (CC0 image courtesy of Cooper Hewitt, Smithsonian Design Museum.)

Born in 1862, Felt had left school at 14 to apprentice in a local machine shop before moving to Chicago six years later.1 He found work there in a “rolling mill”, a factory which rolls metal into different thicknesses and shapes.2 And it in was there, in 1884, that he had the idea to build an adding machine.3

Felt had been using a tool that relied on a series of notches to control its movement, and he wondered if he could use a similar mechanism to drive an adding machine. First, he told himself: “I will make such a machine.” Then, he told a friend: “In ninety days every office in the United States will be doing its calculation by machinery.” A grand ambition, but it would start more humbly. To build a prototype, Felt bought a macaroni box at a grocer’s shop, skewers at a butcher, staples at a hardware store and elastic bands at a bookshop. He worked on his device on Thanksgiving, Christmas Day and New Year’s Day, but it was still nowhere near complete.4

In the event, it would take Felt most of his ninety days just to finish a working prototype. A more functional metal version followed early in 1885; a production-ready machine in the autumn of 1886; and a partnership with a Chicago factory owner in 1887.3

Although the first Comptometer was an adding machine rather than a true calculator, its voluminous keyboard was the key (sorry) to its success. Each digit was handled by a column of keys labelled from 0 to 9, and pressing a key immediately added its value to the running total. There was no crank to turn or lever to pull, and a skilled operator could add an entire multi-digit number by pressing multiple keys at once.5

The keyboard, in fact, was the Comptometer’s chief legacy: many other mechanical calculators adopted it, despite using different internal mechanisms, purely for its familiarity to users. Even the Sumlock Anita, the first electronic calculator, would do the same. The Comptometer cast a long shadow.

Holman, Alfred L. (Alfred Lyman), and Dorr Eugene Felt. A register of the ancestors of Dorr Eugene Felt and Agnes (McNulty) Felt. Chicago, Priv. print. for D. E. Felt, 1921.






Felt, D. E. Mechanical Arithmetic, Or, The History of the Counting Machine. Lectures on Business, Ed. By T. H. Russell. Chicago: Washington institute, 1916.




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