A Sinclair Cambridge calculator with its case. As a sense of scale, the tiles in the background have 5-centimetre (2.0 in) long edges
|Release date||August 1973|
|Power||AAA batteries, PP3 battery|
|CPU||General Instruments Microelectronics GI-C550 (Cambridge), National Semiconductor MM5799EHY/N and DS7784N (Programmable)|
|Display||8-digit LED character display|
|Weight||3.5 ounces (99 g)|
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 50x111x28mm.
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.
A later model, the Sinclair Cambridge Scientific, was developed, and launched in March 1974 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 some common scientific functions (sin, cos, tan, etc.).
The other calculators in the range were 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 Cambridge Programmable (sold in the U.S as the Radio Shack EC-4001) was released in 1975. It lacked accuracy in many of its scientific functions, some yielding only four significant digits. It featured a single memory register and a limit of 36 program steps, along with a conditional jump instruction. The Programmable came with a program library consisting of 4 books, covering general functions, finance & statistics, mathematics, physics & engineering and electronics.
The Cambridge Programmable was superseded by the Sinclair Enterprise, which allowed 80 program steps.
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