In 1623 Professor Wilhelm Schickard (1592-1635) of Tübingen constructed the first calculating machine in the world with a mechanical tens-carry mechanism. He was a mathematician, geodesist and astronomer and as such was very interested in the problem of how to prevent errors when calculating numerically. To this end he invented a mechanical calculating machine of which he built two models – one for himself and the other for a friend, the astronomer Johannes Kepler. As both machines were lost during the Thirty Years’ War, their construction details remained unknown for a long time. It was not until the 20th century that a careful study of all the construction details and sketches which Schickard had sent to Kepler made it possible to build an exact copy of the Schickard machine. This initiative was due to Professor Baron v. Freytag Löringhoff of Tübingen, who also built this replica for the Arithmeum. The machine is in two parts: the lower one is for addition and subtraction (a system of cogwheels with automatic tens-carry) and the upper one for multiplication and division (comprising an adaptation of Napier’s rods consisting of six rotating cylinders akin to the arrangement found in Schott’s box). A register can be used as a revolution counter. As only the lower part has an automatic tens-carry mechanism, the Schickard machine is the first fully functional two-species calculating machine. Multiplication and division can, however, easily be performed by using the lower part in conjunction with the registry (revolution counter).