## The mechanical calculator for all four arithmetic operations by Axel Jacob Petersson

Axel Jacob Petersson’s calculating machine from 1871 is the first one to use a single central stepped drum. This special quality made it possible to build the machine with a diameter a lot smaller than all previous machines for all four basic arithmetic operations. It is true that the machine – which was only a prototype – still had certain problems in putting this idea into practice efficiently. However, its aesthetics and its elaborate solutions can be studied in detail in the animated video that Steffen Metzner made as a “Projektgruppenarbeit” for Professor Dr. Ina Prinz during his studies of Computer Science. Enjoy the exploration of this unique artefact in the history of mathematics!

We would like to thank the Norwegian Museum of Science and Technology in Oslo that supported us in a very friendly way in the making of this project. We are especially grateful that after the joint restoration of Petersson’s two calculating machines by the restorers Endre Fodstad, Norwegian Museum of Science and Technology, and Ingo Laubach, Arithmeum, we can now display the prototype of this calculating machine as a loan from the Norwegian Museum of Science and Technology in the Arithmeum. Hopefully, you can see the original in a different light when you admire it in the Arithmeum in the future.