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".
This is not true since there were earlier calculators that would fit in a small pocket (for example the Busicom LE-120A "handy"). However, the Sinclair Executive, shown on the left, was the first slimline calculator and when launched 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.