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Sinclair Wrist Calculator

Wrist calculator

Sinclair Wrist Calculator

Display is 8 digits, red LED.

4-functions, %, memory, square root.

8.1v (6x mercury cells).

Integrated circuit - Mostek MK50321N, here date coded mid-1976.

47 x 45 x 18 mm (1.9 x 1.75 x 0.7 ins).

Made in England by Sinclair Instruments Ltd. (a company formed by Clive Sinclair as Sinclair Radionics started to have financial difficulties, later becoming Science of Cambridge Ltd.)[1].

Launched in February 1977.

Was available only as a self-assembly kit, by mail order from Science of Cambridge, previously Sinclair Instrument Ltd., which had been founded by Clive Sinclair and to which he moved from Sinclair Radionics.  (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.)

There are two versions of this calculator, see photograph of the later version below.

Total price was only £11 Sterling (about US$20).

Although combined watch-calculators became very popular, starting with LED display models such as the Pulsar and Compuchron, only two models of pure wrist calculator are known, the Sinclair and the Quik Check.

Clive Sinclair was always interested in making tiny versions of common electronic items.  Here, into the smallest practical volume he managed to squeeze the LED display and chip used in other Sinclair calculators (the Sinclair Cambridge Memory and Cambridge Universal), which were then becoming obsolescent.

Wrist calculator version 2

Second version of the wrist calculator, advertised in November 1977 as "Now even better, even more powerful"

Note the extra functions below the keys as well as above, and the function switch on the keyboard, rather than out of sight on the lower edge of the body.

With instructions

Wrist calculator and assembly instructions.


Wrist calculator main components.


Wrist calculator main components showing the Mostek MK50321N integrated circuit occupying most of the small circuit board.


  1. Adamson, I., and Kennedy, R., (1996) "Sinclair and the 'Sunrise' Technology", Harmondsworth, Penguin Books Ltd., ISBN 0-14-008774-5.

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