The Cambridge &
Cambridge Scientific

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.