Sinclair Radionics, Ltd.
Huntingdon, Cambs., UK
Clive Sinclair is a British electronics genius. He founded his company in the early 1960s and introduced very innovative micro radios and audio equipment. In 1972 he amazed the world with the Sinclair Executive calculator which was only 9mm (0.4") thick and ran off button cells. A range of calculators followed, but Sinclair left the calculator business in 1979 to concentrate on other products, such as the home computers and micro-televisions. See the article "Clive Sinclair and the Pocket calculator" in the Collecting Calculators section of this site.
Clive Sinclair was very innovative in the field of consumer electronics and, for many years in Britain, was widely known as "the man who invented the pocket calculator".
Whichever way you define the size of a pocket this is not true, but when the Sinclair Executive, shown on the left, was introduced in July 1972 it caused a sensation because it was the world's thinnest calculator by a long way.
The later Cambridge models were also very small and generally crammed many functions into their small size. However, the smart design of some of these, the "pregnant" models, was destroyed since they required a large bulge in the back of the case to take a 9v PP3 battery instead of the earlier AAA pen-light cells.
The Sinclair name is associated with several companies. Nearly all of the calculators were produced by Sinclair Radionics Ltd., though the Wristwatch calculator was produced by Sinclair Instruments Ltd. There is a brief history of Clive Sinclair, his companies, his calculators, and other products in the article Clive Sinclair and the pocket calculator in the Collecting Calculators section of this site.
Sinclair calculators are known for their innovative and often elegant designs.
Source : vintagecalculators.com