Sinclair Cambridge pocket calculator, by Sinclair Radionics Limited, Cambridgeshire, England, 1973

Sinclair Cambridge Electronic Pocket Calculator. This was one of a series of small calculators developed by British inventor, Sir Clive Sinclair (b.1940) in the early 1970s and the first that were designed to be small and light enough to fit in the pocket. It was sold both as a kit and fully built. Although it was expensive when it was first produced, its price soon dropped from £29.95 when first introduced in 1973 to below £15 in 1975. The Cambridge calculator was small, even by modern standards, weighing only 3.5oz (99g). It suffered from a design flaw; after a certain amount of use, it was impossible to turn off due to oxidation of cheap components used in the switch contacts.