Trial model for part of Babbage's difference engine, on board

This trial model for part of Babbage's Difference Engine No. 1 was built by Henry Prevost Babbage (1824-1918) from the designs of his father, British computing pioneer Charles Babbage (1791-1871). This was one of approximately six demonstration models of the calculating mechanism of Engine No. 1 built by Henry after his father's death, using unused parts from the original. Charles Babbage conceived the idea of building an automatic calculating machine which would eliminate the inaccuracy that occurred when compiling mathematical tables by hand. Never built during Charles Babbage's lifetime, it was a decimal digital machine - the value of a number being represented by the positions of toothed wheels marked with decimal numbers.