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Sinclair Cambridge
1973-74


Size: 50 mm x 111 mm x 28 mm (2" x 4.4" x 1.1").

Display: 8 digits, red LED

Power: AAA or PP3 batteries


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The Sinclair Cambridge, the first in a range of seven calculators, was launched in August 1973. It was small, even by today's standards, weighed less than 3.5 oz and sold at £29.95 + VAT or, in kit form, at £24.95 + VAT. A "valuable book" [sic] was supplied with it to explain how to use the Cambridge to handle advanced functions such as trigonometry, nth root extraction, compound interest and the like.

Eight months later in March 1974, the Cambridge Scientific was launched at a price of £49.95 (£5 cheaper than its nearest rival from Hewlett-Packard). As the name suggests, it was a development of the Cambridge, using the same case, with the addition of a number of common scientific features (sin, cos, tan etc).

The other calculators in the range comprised the Cambridge Memory, Cambridge Memory % (which came in two different versions), Cambridge Programmable (marketed in the United States as the Radio Shack EC-4001), Cambridge Scientific, Cambridge Scientific Programmable and Cambridge Universal. The later Sinclair Scientific first appeared in a case derived from that of the Cambridge, but it was not part of the same range.

The Cambridge calculators suffered from a near-fatal design flaw which resulted from the cheapness of the components - after some use the calculator would be impossible to switch off. This resulted from the material used to make the switch contacts. Most circuit board connectors are made of gold-flashed nickel (the Spectrum edge connector is a prime example) and the prototype Cambridge was no exception. However, when full production began, it was decided to make use instead of cheaper tin-coated nickel connectors. This grew a soft oxide layer (not a problem with gold, which doesn't oxidise), with the result that after the switch had been slid backwards and forwards a few times the surface of the tin would smear across the insulation so creating a permanent circuit. Having to take the battery out to cut the power every time one had finished using the calculator was, to say the least, inconvenient.

As with all of the Sinclair calculators, the Cambridge's display used light-emitting diodes. This made it a power-hungry device, forcing a rather messy design compromise on the Cambridge Memory % Type 2 and Cambridge Programmable. The power demands of both devices required the use of a PP3 battery, creating the distinctive "pregnant" appearance of the case (right).


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Chris Owen 1994-2003