Schuster III

So far as is known today, the Franconian watchmaker Johann Christoph Schuster (1759 - 1823) built three cylindrical calculating machines. The first, dating from 1789-1792 and possessing eleven places, was built exactly according to the design of the Hahn Calculating Machines – it is now in the Deutsches Museum, Munich. The second, dating from 1805-1820 and possessing nine places, is somewhat smaller than the first and features the well-known setting dials of the Müller Machine – it is now also in the Deutsches Museum, Munich, and there is also a Replica in the Arithmeum. The third, dating from 1820-22 and possessing ten places, first became publicly known through an auction in London in 1993. It was acquired by the Arithmeum in 1999. The inscription on the top-plate reads “Rechnungs Maschine von Johann Christoph Schuster zu Ansbach in Franken angefangen 1820 vollendet 1822“. The ten setting wheels are turned by means of laterally placed serrated knobs, the entered digits appearing in windows below which there are short cylinders with inscribed numbers on their curved surface. The result mechanism and revolution counter comprise the central rotatable part of the machine; both have ten places. The larger enameled numbered discs belong to the result mechanism and the smaller ones to the revolution counter. The black and red numbers of the larger discs are for multiplication and division, respectively, and a corresponding inscription next to the units-disc reads “RothSubtr: u: Div: Schwarz Add: u: Mult:“. The outer ring bears the inscription “Die Scheiben Zahlen sind zu der Rechnungsart die Richtung“. The discs of the result mechanism are inscribed as follows: Einer, Zehen, Hundert, Tausend, 10 Tausend, 100 Tausend, Million, 10 Million, 100 Million, 1000 Million. The discs of both mechanisms have serrated knobs for direct setting as well as for resetting to zero. The inner unit can be rotated for different decimal places and fixed by means of a spring-loaded rod. The crank can only be turned in the clockwise direction. The current position of the revolution counter is indicated by a centrally mounted pointer. The essential mechanical works, including the stepped drums and tens-carry mechanisms, follow Hahn’s designs. This machine was developed and built when, at the same time, the Frenchman Charles Xavier Thomas made his first attempts to develop a commercially usable stepped drum machine. It is very likely the last machine of the pre-industrial era.