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Charles Babbage's design for the firstautomatic mechanical calculator. The Difference Engine was aspecial purpose device intended for the production ofmathematical tables. Babbage started work on the DifferenceEngine in 1823 with funding from the British Government. Onlyone-seventh of the complete engine, about 2000 parts, wasbuilt in 1832 by Babbage's engineer, Joseph Clement. This wasdemonstrated successfully by Babbage and still worksperfectly. The engine was never completed and most of the12,000 parts manufactured were later melted for scrap.It was left to Georg and Edvard Schuetz to construct the firstworking devices to the same design which were successful inlimited applications. The Difference Engine No. 2 was finallycompleted in 1991 at the Science Museum, London, UK and is ondisplay there.The engine used gears to compute cumulative sums in a seriesof registers: r[i] := r[i] + r[i+1]. However, the additionhad the side effect of zeroing r[i+1]. Babbage overcamethis by simultaneously copying r[i+1] to a temporary registerduring the addition and then copying it back to r[i+1] at theend of each cycle (each turn of a handle).Difference Engine at the Science Museum(http://nmsi.ac.uk/on-line/treasure/plan/2ndcomp.htm#babbage).