The distinguished mathematician and philosopher Gottfried William Leibniz started thinking about stepped drum calculating machines in the 1670s, and an eighteenth century instrument built on his design survives. However, it was the French insurance executive Charles Xavier Thomas (1785–1870) who invented and sold the first commercially successful calculating machine. Proposed in 1820, it would sell successfully from about 1850.
Thomas’s calculating machine, which he dubbed the arithmometer, had cylindrical brass drums, each with nine teeth that varied in length. If a setting lever was at “9”, it engaged nine teeth, at 8, eight teeth and so forth. This stepped drum mechanism would be modified over time, with different metals used for the stepped drums, much of the drum cut away, and different arrangement of the teeth on the gears. Nonetheless, the stepped drum survived as part of some calculating machines as long as they were manufactured.
