Sinclair Cambridge electronic calculator, 1973.

This model was one of a series of small calculators developed by the British inventor, Sir Clive Sinclair (b 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.