Toller oller Rechner aus dem Jahr 1784 von Johann Helfrich Müller aus meinem Geburtsort Darmstadt. Der Mann war vor allem Architekt und Stadtplaner und hat unter anderem den alten Darmstädter Marktplatz gestaltet, über den ich jahrelang gelatscht bin, weil ich vor drölftausend Jahren dort mal in 'nem Plattenladen gearbeitet hatte. Vintage, doh!
After about three months of designing, in June, 1782, the project was ready and Müller gave the drawings to a clockmaker in Darmstadt, with the order to make the machine in metal. The work was taken over by a pair of journeymen in the same trade and on the 20th of June 1784, the machine was ready. On 24th of June, 1784, the 14-digit calculator (see the upper image) was demonstrated in the Göttingen Academy of Sciences, which appointed him as a correspondent.
Müller's calculating machine is very similar to the machine of Hahn and was based on the Stepped Drum of Leibniz, but it is larger (285 mm diameter, 95 mm height, weight 15.4 kg). It was in the form of a round box with a handle placed centrally and the number wheels concentrically arranged around the handle. It could calculate with 14 figures and its number and gear wheels could be altered to enable it to operate with non-decimal number systems.