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    'Addiator' calculating machine, c 1924.

    Addiator' decimal adding machine with stylus and pencil on metal stand. Made by the Addiator-Gesellshaft Company of Berlin, Germany, the 'Addiator' was a relatively late mechanical calculator. It uses a chain mechanism, a stylus to add or subtract an

     
    Exactus stylus-operated adding and subtracting device, 1955-1965.

    Exactus stylus-operated adding and subtracting device, with swivelling half plate for add and subtract options, marked "Mini-Add Made in England", c. 1950. The Exactus is one of several simple stylus-operated calculators to have been popular in the

     
    French sector, 1751-1774.

    Brass French sector by Canivet, Paris, 1751-1774. French sectors are less complicated than English sectors. They are also used for calculations involving proportions of length, area and volume.The lines radiate from the centre of the hinge.

     
    Klein bottle, 1995.

    A single surface model made by Alan Bennett in Bedford, 1995. It consists of a parallel sided coil with one piercing of the return tube which when theoretically cut gives a pair of 15-twist Mobius strips. A Klein bottle has no edges, no outside or in

     
    A stchoty, Russian abacus, early 20th century.

    Stchoty (Russian form of Abacus), early 20th century. The stchety has horizontal rows of beads rather than vertical as in the Japanese abacus. It is specifically for counting rubles and kopeks. The lower three rows are for the kopeks. The rest positi

     
    Robertson's 'Rapid Calculator', c 1910.

    Robertson's Rapid calculator, pat no. 5871,1910. Made by the Robertson Rapid Calculator Company of Glasgow, this was one of several large-scale ready reckoners to be developed in the first decade of the 20th century. This form of ready reckoner place

     
    Set of Napier's rods, 1770-1790.

    Set of Napier's bones, in wooden case with trade label of "J. Imison, Clock & Watch Maker, Optician, &c., No. 58 Hay-market, London", late 18th century. Napier's bones were invented in 1617 by Lord Napier of Murchiston, the inventor of logarithms, as

     
    The 'Tachylemme' ready reckoner, c 1876.

    "Tachylemme" of C.L.Chambon, c.1876. This instrument shows the daily interest on sums of money at various rates.

     
    Gunner's callipers, early 18th century.

    Gunner's callipers by Thomas Wright, early 18th century. The callipers can be used as shown to measure the diameter of cannon balls, or with crossed arms to measure the bore of a cannon. The arms are inscribed with tables containing information relat

     
    Pascal's calculating machine, 1642.

    Replica made by E. Rognon, Paris of Blaise Pascal's first calculating machine of 1642, held by the Conservatoire National de Art et Metiers, Paris.The original machine was completed in 1642 when Pascal was only 19, to help his father in business. It