Facsimile of Stanhope's 1775 calculating machine, copied from the example at the Science Museum.

Facsimile of Stanhope's 1777 calculating machine, copied from the example at the Science Museum.

Thomas de Colmar arithmometer, made in around 1875. Colmar introduced his first version in 1820 and then made many improvements to what became the first commercially successful calculating machine. The design was not sufficiently reliable for it to come into common usage until the late 19th century. Despite the improvements, there was still a risk of error in the transcription of the result and the operator needed to understand the mathematical principles involved. The arithmometer is based on the Leibniz stepped reckoner, or stepped drum.

Edmondson's circular calculating machine made by W.F. Stanley in around 1890.

Layton's improved arithmometer, made by C. & E. Layton, 1912.

MADAS Arithmometer, made by H. W. Egli of Zurich.

Model K electric comptometer, made by Felt & Tarrant, USA, c.1950. This machine is adapted for sterling currency with a capacity of £999,999,999:19s:11d.

Brunsviga Mk. III barrel calculating machine, made by Grimme Natalis & Co, supplied by Block & Andersen in around 1895.

Burroughs Class 3 adding/listing machine, made in Canada, c.1910. The capacity is £999:11:113/4d. There is a facility for taking both totals and subtotals, and also a repeat key to prevent keys having to be reset if several identical sums are to be added.

Unsigned comptometer supplied to the Prudential Assurance Company Ltd. Probably German.

Fuller spiral slide rule by W.F. Stanley in a wooden case with instructions, 1897.

Ready Reckoner for calculating workmen's wages by General Company of Ready Reckoning Machines, sole agent Deane, Dray & Co., London.

Model of human brain, made by Adam, Rouilly Ltd, London, c. 1965.