Sinclair Cambridge Scientific Calculator
The Sinclair Cambridge was a small pocket-sized calculator manufactured from summer 1973 by UK company Sinclair Radionics. It was available both as a kit to be assembled by the purchaser, and assembled. The range ultimately comprised seven models, the original "four-function" Cambridge, which carried out the four basic mathematical functions of addition, subtraction, multiplication, and division, being followed by the Cambridge Scientific, Cambridge Memory, two versions of Cambridge Memory %, Cambridge Scientific Programmable and Cambridge Universal.
The Cambridge had been preceded by the Sinclair Executive, Sinclair's first pocket calculator, in the summer of 1972. At the time the Executive was smaller and noticeably thinner than any of its competitors, at 56x138x9mm, fitting easily into a shirt pocket.
The Cambridge was extremely small for a calculator of the time: it weighed less than 3.5 ounces (99 g) and its size was 50 x 111 x 28 mm.
A major factor in the Cambridge's success was its low price; the Cambridge was launched in August 1973, selling initially for GB£43.95. In January 1974 the Cambridge was priced at £32.95 (£29.95 + VAT) fully assembled or £27.45 (£24.95 +VAT) as a kit, bundled with an extensive manual detailing how to calculate functions such as trigonometry, n-th root extraction and compound interest on the device. Initially power was supplied by 4xAAA batteries.
The use of cheap components was an important contributor to the unit's cost. A common failure mode was breakage of the battery contacts,making it impossible to switch the calculator off, due to the use of switch contacts made of nickel coated with tin, rather than the gold; tin, unlike gold, produces an oxide layer when exposed to air which spreads across the insulation over time as the switch is operated, short-circuiting the switch.
The Cambridge used light-emitting diodes for its display. On later scientific variants the power draw for the display required a larger PP3 battery, creating a bulge in the lower rear casing of the appliance.
Numbers were displayed on the 8-digit LED display (made by National Semiconductor) in scientific format with a 5-digit mantissa and a 2-digit exponent.
Our Sinclair Cambridge Scientific together with the original hard case were very kindly donated By Julian Bryant.
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This exhibit has a reference ID of CH21989. Please quote this reference ID in any communication with the Centre for Computing History.