An early example of the Comptometer, with 72 numbered keys. The top of box has a plate engraved; 'Trade Comptometer mark, Patd. July 19th 1887, - Oct 11th 1887, Jan 8th 1889, June 11th 1889, Nov 25th 1890, Dec - 15th 1891, Felt & Tarrant Manufacturing Co, Chicago'. The Felt and Tarrant Comptometer was one of the first generation of mas-produced office calculators.
© Science Museum / Science & Society Picture Library