The calculating machine for all four arithmetic operations “Hamann Manus“, named after the calculating machine inventor Christel Hamann, was launched by the company DeTeWe in 1925. It is a calculating machine with a switching latch mechanism, and Hamann was the first to successfully use this mechanism in calculating machines manufactured in series production. The switching latches that Dietzschold and Weiss had developed before to mechanically store numbers never got beyond the stage of a prototype. Still, the basic idea was similar: developing a calculating machine that requires only simple components and operates with as little attrition as possible. The characteristics of this brilliant mechanism can be easily understood from the 3D animation of the Hamann Manus machine that Computer Science student Xenia Ewert made as part of her bachelor’s thesis about the history of mechanical calculation for Professor Dr. Ina Prinz. Enjoy your meeting with this small calculating machine.