Dear all: To this day, it is unknown how the Inka calculated with their mysterious abacus, the Yupana. Perhaps of interest to you: Bruderer, H. (2024). How did the Inka Calculate? The Yupana, a Mysterious Peruvian Abacus. Zenodo. https://doi.org/10.5281/zenodo.13174318 https://zenodo.org/doi/10.5281/zenodo.13174317 Bruderer, H. (2024). Yupana, ein rätselhafter peruanischer Abakus. Wie haben die Inka gerechnet? Zenodo. https://doi.org/10.5281/zenodo.13175212 https://zenodo.org/doi/10.5281/zenodo.13175211 And: The fake chess-playing automaton: Technical Marvels, Part 5: Chess Automatons – Communications of the ACM Chess robots, from a fake automaton to a world champion-defeating program. Best wishes, Herbert Bruderer -- Bruderer Informatik Seehaldenstrasse 26 Postfach 47 CH-9401 Rorschach Switzerland Telefon +41 71 855 77 11