Some people are so poor, all they have is money.

*Bob Marley*

At the end of the 1770s, the Württemberg pastor and genius engineer Philipp Matthäus Hahn hired for his workshop in Kornwestheim as an apprentice the young Franconian Johann Christoph Schuster (1759-1823). Schuster remained in Hahn’s workshop for two and a half years, then in 1785 he married his sister Maria Katharina Jacobina and started his own workshop.

Just like his mentor Hahn, Schuster became a very good engineer and after the early death of Hahn in 1790 he continued his deed, manufacturing quite a few clocks and calculators, improving Hahn’s designs. To the present time survived three of Schuster’s mechanical calculating machines and four clocks.

Schuster commenced his first calculating machine according to Hahn’s design in 1789 (probably under the supervision of Hahn), and it was completed in Uffenheim in 1792 (Hahn had died two years earlier). From 1805 Schuster developed his own calculating machine in Ansbach (four-species machine, relay roller principle), which is also based on Hahn’s design but is more compact and easier to use. It was completed in 1820 and can be seen now in the collection of the Deutsches Museum in Munich (just like the first Schuster calculating machine), bought in a Christie’s auction in 1993 for 17.5 million DM. In 1822 Schuster completed his third and last calculating machine, which is now in the Arithmeum Museum in Bonn. All his calculators are still working perfectly today. The first calculator has 12 digital positions, the second has 9 digital positions, the third has 10 digital positions.

The first calculating machine of Johann Christoph Schuster (see the upper image) is a 12-place brass and steel device with dimensions: 29.5 cm diameter x 10.8 cm high, weight: 8.1 kg, made 1789-1792 in Uffenheim. The machine consists of 1025 handcrafted individual parts (including gears, levers, pawls, and springs).

The second calculating machine of Schuster (see the lower image) is much smaller: it is a 9-place device with dimensions: 18.5 x 21 cm, weight: 4 kg, made 1805-1820 in Ansbach (after its completion in 1821, it was acquired by the Bavarian state for 1000 guilders and exhibited in the Polytechnic Collection, which has existed since 1822).

Its construction is basically the same as the first machine, but it has an improvement on the setting mechanism, where the racks are similar to Müller‘s calculating machine from 1783, and are moved using rotary knobs.

The third calculating machine of Johann Christoph Schuster (see the upper image) is similar to the second. The ten digits of the setting mechanism are operated with knurled nuts, whereby the setting of a number can be checked in a control mechanism with dials. The result mechanism and the revolution counter are located in the central, rotating part of the machine, they are each ten digits. The larger enameled dials belong to the result mechanism, and the smaller ones to the revolution counter. The black and red digits in the result set are intended for multiplication and division, respectively (red digits present complementation to 9 of black digits, e.g. over black 5 is inscribed red 4). There is a corresponding label next to the units: “Roth Subtr: u: Div: Black Add: u: Mult:” (in English: Red for subtraction and division; Black for addition and multiplication.)

The following text is engraved on the setting ring: “The numbers on the discs are the direction for the type of calculation”. The position values of the result work are engraved as follows: One, ten, hundred, thousand, 10 thousand, 100 thousand, million, 10 million, 100 million, 1000 million. For each of the two places, there is a direct setting using knurled nuts; these also serve to reset the relevant place. The inner unit, which can be rotated for the decimal shift, is fixed by means of a latch. The crank may only be turned in one direction (clockwise). The respective arithmetic position of the revolution counter is indicated by a pointer. The main mechanical devices, including staggered rollers (stepped drums) and the two-stage tens transfer, correspond to those of Hahn’s construction.

#### Biography of Johann Christoph Schuster

Johann Christoph Schuster was born on 8 October 1759 in Westheim (Middle Franconia, Bavaria). He was the son of Lorentz Schuster (died 1785), a local farmer, and Anna Elisabetha Fröhlich (died 1762).

We don’t know anything about his childhood, but around 1777 he was bound apprentice to Philipp Matthäus Hahn, a pastor and owner of a mechanical workshop in Kornwestheim. Schuster remained in Hahn’s workshop for two and a half years, then returned to his father’s farm, but continued his occasions with machines, keeping a connection with his mentor. In 1785 Schuster married Maria Katharina Jacobina (1759–1812), a half-sister of Hahn. They had three sons (two of them died early) and five daughters.

After his father’s death in 1785 Schuster took over his farm and also opened in the village a workshop in which he made clocks, sundials, earth and celestial globes, and calculating machines. From 1786 he was a freelance watchmaker, first in his native Westheim and then in Uffenheim. Schuster moved to Ansbach in 1797 and became a master member of the local watchmaker’s guild and received permission to work as a “mechanic and watchmaker” in Ansbach, Uffenheim, and Erlangen. He ran a workshop in Ansbach, the seat of Hohenzollern princes (known as margraves), and stayed there working as a mechanic and court watchmaker until his death.

Besides the above-mentioned calculators, four other masterpieces of Schuster survived to our time: two pocket watches (now in Württembergisches Landesmuseum Stuttgart and Stadtmuseum Ansbach) and two double globe clocks (in Mathematisch-Physikalischer Salon Dresden, and in a private collection).

Johann Christoph Schuster died on 7 September 1823 in Ansbach.