|The Sinclair Cambridge was launched
in August 1973. It was small, even by today's
standards, at only 4.5" x 2" x
0.7", 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 Sinclair Scientific - or 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. Its most notable innovation was the way in which it packed 12 functions onto just four upper- and lower-case keys, a trait which was to come fully to fruition with the ZX machines the following decade. It was also the first Sinclair machine to use a semi-custom chip (from Texas Instruments) and was noteworthy for using the rather bizarre reverse Polish notation. This meant that, for instance, to add 2 and 4, you had to enter 2, then 4, then the + symbol. Although this was the easiest way to present data to the chip, the human users were rather less impressed.
Both Cambridge models 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.