Figure wheel and drawing by Charles Babbage, 19th century.
© Science Museum / Science & Society Picture Library
Figure wheel on a drawing by British computing pioneer Charles Babbage (1791-1871) of the Difference Engine No 2. This engine was conceived in 1821 in an effort to mechanise the production of mathematical tables. It was designed to calculate a series of numerical values and automatically print the results. It calculated using the 'method of finite differences'; a well-used principle of the time. The advantage of using the method of differences is that it eliminates the need for multiplication and division in the calculation of a particular clas of mathematical functions called 'polynomials'. The Difference Engine only used addition, which is easier to mechanise than multiplication and division.