Sinclair Cambridge
Programmable Pocket Calculator
The Sinclair Cambridge series was introduced by Sinclair Radionics in the summer of 1973, eventually growing from a basic four-function model into a range of seven variants. The Programmable version appeared in 1975 and was one of the earliest affordable programmable pocket calculators on the market.
Technical specifications: The display was an 8-digit red LED unit manufactured by National Semiconductor. Inside, the calculator used National Semiconductor MM5799EHY/N and DS7784N integrated circuits. It featured a single memory register, a maximum of 36 program steps, and a conditional jump instruction. Its dimensions were a compact 50 Ă— 111 Ă— 28 mm.
Power supply and design: While the original Cambridge ran on four AAA batteries, the Programmable required a 9V PP3 battery, which created a distinctive bulge on the back of the case — playfully referred to as the "pregnant" design by enthusiasts.
Accuracy and limitations: The scientific functions had limited precision, yielding only four significant digits in some cases. This was a weak point compared to competitors, but the low price more than made up for it.
Program libraries: The calculator came with a four-volume program library covering general/finance/statistics, mathematics, physics/engineering, and electronics.
Sales and distribution: In the United States it was sold under the name Radio Shack EC-4001, as Sinclair supplied the Radio Shack electronics chain. The Cambridge Programmable was eventually succeeded by the Sinclair Enterprise, which offered an expanded capacity of 80 program steps.
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