Wilhelm Schickard (1592-1635) had been Professor of Hebrew at the University of Tübingen since 1619 and succeeded his teacher Michael Mästlin as Professor of Mathematics, Astronomy and Geodesy in 1632. As a 25-year-old deacon in Nürtingen, he got to know Johannes Kepler. For Kepler, with whom he corresponded throughout his life, he made drawings for his Harmonices mundi libri V (1619) for the Tabulæ Rudolphinæ (1627).
In 1623, he constructed the world's first digital calculating machine, which he himself named Rechen-Uhr. It was a six-digit four-species machine with a mechanical tens transfer unit. He only had two copies made, one of which was intended for Kepler and was burnt shortly before completion. His own copy was probably lost in 1634 in the course of the plundering by the imperial troops.
The complete description of the instrument as PDF for download
