After having presented the “Hamann Manus” machine, a four-species calculating machine with a switching ratchet mechanism, as our weekly animated video last week, we will now show you an earlier invention by Christel Hamann that emphasizes what a genius inventor he was in the field of calculating machine technology. The designer from Berlin invented the compact cylindrical four-species calculating machine with a central stepped disc around 1905 and described it in patents. A first variant of a calculating machine construction with a central stepped drum by Hamann and Haack was already shown at the world exhibition in Paris in 1900. The machine – that was first called “Gauss” and then later “Mercedes” in its improved version – can be seen as a precursor of Curt Herzstark’s “Curta”, together with Axel Jacob Petersson’s “Calculator”. A turn of a crank moves the unique central stepped disc past the gear wheels of the result mechanism that are arranged in a radial way above it, thus transferring the number that was entered into the result mechanism. Unlike the earlier “Gauss” machine, the “Gauss-Mercedes” has a complementary switching disc that makes it possible to solve subtraction and division in a purely mechanical way, too. This disc might have been the source of inspiration for the development of the complementary stepped drum in the Curta machine. The distinguishing mark on the outside of the Gauss-Mercedes is the additional switch “Add./Sub.” next to the crank. The development process of the machine involved geoscientists among others, who were very much interested in a mobile calculating machine to be used in the field. Therefore, there were two versions of the machine: one with a cast-iron stand and one with a handle to be held with one hand. As part of his bachelor’s thesis with Professor Dr. Ina Prinz, Steffen Metzner made a 3D animation of this calculating machine and explained it in an excellent didactical way and with great attention to detail. We hope to be able to share the fascination for this complex calculating machine with you via this video.