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Calculator. Engraving of German engineer Jacob Leupold's (1674-1727) mechanical calculator design of 1727. The calculator contained a number of toothed wheels (in the upper frame). Each cog had ten teeth which each represented a number between 1 and 9. The cogs were connected through a complex series of gears so that the complete revolution of one cog led to another cog moving on by one notch. To perform a calculation the handle at the centre of the circular calculator face was revolved a certain number of times. The calculator could do additions and multiplications. Leupold's design was never built.
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