Today in 1887, Dorr E. Felt was granted a second patent for the Comptometer, a mechanical calculator.
Adding machines were used by accountants, bankers and merchants to add and subtract, multiply and divide, often with a paper tape record of the calculation. Constantly improved, the Comptometer was manufactured and successfully sold until the mid-1970s, when the transition from mechanical and electromechanical devices to electronic devices was completed.
In 1916, Felt gave a lecture on “Mechanical Arithmetic, or the history of the counting machine,” in which he recalled putting together the first Comptometer:
When I first thought of making a calculating machine, I was working in a machine shop. I was running a planer. A planer has a tool that runs back and forth across one or more notches according to how you adjust it. I said, "Why can't that be used for counting?"
I thought about it all night, and pretty soon I said, "I will make such a machine."
I had a friend who was an electrical engineer, and I told him what I was going to do, and said: "In ninety days every office in the United States will be doing its calculating by machinery."
So I went to the grocery and bought a macaroni box to make the frame of. I went to the butcher and bought skewers to make the keys of, and to the hardware store and bought staples, and to the bookstore and bought rubber bands to use for springs. I went to work to make a calculating machine, expecting to have thousands in use in ninety days. I began on Thanksgiving Day, because that was a holiday, and worked that day, and Christmas and New Year's, but I didn't get it done in three days. It was a long time before I got it done.