The mechanical calculator was born on 11 October 1887. But that is the day of the patent. In reality, the first prototype was three years earlier. It was told by the inventor himself, Dorr Eugene Felt, who was just 23 when he invented the Comptometer (this is the name). So we’re in Chicago. Here’s how it went: “We were on the eve of Thanksgiving Day of 1884 (the end of November, ed), and I had decided to use that party to build a wooden model. So I went to a grocery store and picked out a box that seemed to be just the right size. It was a packet of pasta, which is why I have always called that model “macaroni bx model”. For the frets, I got some meat skewers from the butcher in the corner and clips from a hardware store and an assortment of rubber bands to make springs. When Thanksgiving came, I got to work right away, mostly using a switchblade. I soon realized that I would need better components than the ones I had chosen and when evening came I realized that what I was planning to build in one day was far from finished. Finally I decided to make some metal parts and finished the model on January 1, 1885 ”.
The first Comptometer patent dates back to July 1887, but on 11 October of that year Dorr Felt completed it with some decisive innovations that would ensure the calculating machine a long and general success: improved versions were produced until 1970. The Comptometer substantially he did additions by showing the results (and he did the multiplications by adding sums).
In an advertising brochure from the early 1900s in Italy, the Comptometer is described as a marvelous machine, “the simplest, the fastest, the most robust”. The recipients are the accountants, who are addressed with an open letter in which they are reminded “that they are waiting for you at home!”. And he closes: “Do not persist, Mr. Accountant, to wear out your brains, to do what the Comptometer does better and faster”.