Sinclair Executive

The Executive was launched in September 1972 at the price of £79.95 plus VAT, equivalent to £1,330 in 2023 when adjusted for inflation. This was around half the price of comparable calculators, but still twice the average weekly wage.^[3][4][5] It was the first pocket calculator, and the first to be mass-produced, and its introduction to the market coincided with a number of other companies entering the calculator market.^[5][6]

The entrepreneur Clive Sinclair, reckoning that the market for "executive toys" was not especially sensitive to price, ordered components for 100,000 calculators.^[7] The Executive was highly successful, and made £1.8 million profit for his company Sinclair Radionics.^[8] It was well received by both domestic and foreign markets, and US$1.5 million worth of Executives were sold in Japan in early 1974 at six times the price of Japanese models.^[9] The parts, consisting of the TMS1802 chip, 22 transistors, 50 resistors and 17 capacitors, cost close to £10, compared with a sale price of almost £80.^[10] The Executive impressed the engineers at Texas Instruments, who had used the same chip to produce a longer and wider calculator that was over three times as thick and a great deal more expensive.^[10] In 1974, sales of the Executive exceeded £2.5 million, and Sinclair was producing 100,000 calculators each month, of which 55% were exported.^[11]

A Sinclair Executive purchased by a Russian diplomat exploded in his breast pocket, allegedly leading to an official Soviet investigation.^[12] It was found that it had been left on by accident, leading to a current drain on the batteries that overheated them until they burst.^[13]

The calculator was significantly smaller than any of its competitors, and the first that could easily be carried in a pocket.^[3][1] According to a Sinclair executive quoted in the Financial Times, "one must always bear a packet of cigarettes in mind as the ideal size", possibly a quip on Clive Sinclair's smoking habit.^[10] The Executive weighed 2.5 ounces (71 g) and measured 56 by 138 by 9 millimetres (2.20 in × 5.43 in × 0.35 in).^[1] The case, designed by Iain Sinclair,^[14] was made of black injection-moulded polycarbonate and required flexible glue to hold the two halves together.^[10]

Design Magazine described it as "at once a conversation piece, a rich man's plaything and a functional business machine".^[12][15] One Executive is on display at the Museum of Modern Art in New York City, and the futuristic design earned it the Design Council Award for Electronics in 1973.^[8][16] It was the first calculator designed for aesthetic appeal, and New Scientist described it as "not so much a professional calculator – more a piece of personal jewellery".^[10]

As well as four-function arithmetic, the Executive could compute squares, reciprocals, and multiply or divide by a fixed constant.^[7] The Executive could display results to two, four, or six decimal places, or use a floating decimal point.^[15]

The calculator was powered by a Texas Instruments TMC1802NC, a metal oxide semiconductor integrated circuit with 7,000 transistors.^[1][7] This CPU normally consumes 350 milliwatts, but by pulsing the power this requirement was reduced to 20 milliwatts.^[7] It was discovered that an early prototype continued to work if the batteries were disconnected and then reapplied quickly enough, as the capacitors in the circuit could hold a charge for up to five seconds.^[17]

Power is supplied to the chip in 1.7-microsecond pulses as determined by the storage time of a control transistor. An oscillator clock operating at 200 kilohertz during calculations and dropping to 15 kHz between each operation means shut-off time ranges from 3.3 microseconds during calculations to more than 65 microseconds between.^[7] The device relies on the capacitance of the chips to store information when there is no power, and 1.7 microseconds proved sufficient for the chip to carry out a single change of state of the electronics.^[7] Any calculation can be done in 1,000 such changes.^[7] This extended battery life to about 20 hours of continuous use with three small hearing-aid batteries, equivalent to about four months of normal usage.^[7][1]

The screen was a monolithic seven-segment gallium arsenide light emitting diode display bought from a Canadian firm.^[18] The small screen reduced the power consumption and material costs,^[15] but it was revised several times in pursuit of lower power consumption, creating reliability problems.^[19]

The Executive Memory was launched in November 1973, with the same dimensions as the original, but with the ability to memorise subtotals from any number of chain calculations.^[20][21][19] There were at least three versions, including the black and white Type 1, and the Type 2 with a gold keyboard.^[20][21] The Executive Memory sold at the lower price of £24.95.^[8]

• Dale, Rodney (1985). The Sinclair Story. Duckworth. ISBN 9780715619018.
• Cockshott, Paul; Mackenzie, Lewis; Michaelson, Gregory (2012). Computation and its Limits. Oxford University Press. ISBN 9780191627491.