Designer of the first functional mechanical calculator, Hahn was born on 25th of November, 1739 in Scharnhausen, Esslingen, as the second of ten children in a family of a pastor. From 1749 to 1754 he attended Latin schools in Esslingen and in Nürtingen. During this time he became interested in astronomical observations and even tried to construct sundials.
From 1756 to 1760 he studied theology at the Protestant theological seminary Tübinger Stift in Tübingen. It is worth noting that some 150 years before Hahn, in the same college, the inventor of the first mechanical calculating machine—Wilhelm Schickard—had also studied theology. Hahn, in contrast to Schickard, later rejected the professorship of mathematics that had been proposed to him there.
