No one knows who built the first adding machine, although many historians believe it was German mathematician Wilhelm Schickard (1592–1635) who first invented a mechanical calculator in 1623 based on Napier’s Bones (see above). Schickard and his family perished from the Bubonic plague. It was not until the mid-20th century that his notes and letters were discovered. They showed diagrams of how to construct his machine. Schickard apparently built two prototypes: One was destroyed in a fire and the other one’s location is unknown, if it survived at all. His device, which he called the “calculating clock,” was able to add and subtract up to six-digit numbers using a mechanism of gears and wheels.

But not all historians credit Schickard. Some believe that there was an even earlier attempt at mechanical computing by Leonardo da Vinci (1452–1519), who also apparently designed an adding machine. Some of his notes were found in the National Museum of Spain in 1967 and describe a machine bearing a certain resemblance to Pascal’s machine (see below).