Sinclair Cambridge pocket calculator, 1973.
© Science Museum / Science & Society Picture Library
This model was one of a series of small calculators developed by the British inventor, Sir Clive Sinclair (1940-) in the early 1970s. These were the first calculators that were designed to be small and light enough to fit in the pocket. This Cambridge calculator was sold both as a kit and fully built. Although it was expensive when it was first produced, its price soon dropped. When first introduced in 1973, the cost was £29.95, but by 1974 a built unit cost £21, and a year later the price had fallen to below £15. 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, the calculator was imposible to turn off due to oxidation of cheap components used in the switch contacts.