Home > British Calculators > Sinclair

Sinclair Executive

Sinclair Executive

There are at least two versions of the Sinclair Executive, with different keyboard markings.

Display is 8 digits, red LED.

4-function.

5.4v (4x button cells).

56 mm x 138 mm x 9 mm (2.2" x 5.5" x 0.4").

Introduced August 1972.

Made in England

The incredibly small thickness (see Executive Memory) for this stage in calculator development was attained by using button cells as the power source.
To achieve the low power consumption needed to employ button cells, with their low capcity, the electronics is pulsed - not recommended by the manufacturer, but it works.
The keypad uses a very thin plastic membrane moulding to keep the thickness down. The actual keys are the tiny buttons in the centre of each pad area.

The incredibly small thickness for this stage in calculator development was attained by using button cells as the power source.
The low power consumption needed to employ button cells with their low capcity was attained by pulsing the electronics - not recommended by the manufacturer, but it worked.
The keypad uses a very thin plastic membrane moulding to keep the thickness down. The actual keys are the tiny buttons in the centre of each pad area.

This was the first Sinclair calculator. It was one of the smallest calculators of the time and certainly the thinnest.

The journal New Scientist noted:
"Just as the price war in electronic calculators was reaching its peak, a Huntingdon hi-fi maker has stepped in with a smaller rather than cheaper unit. Sinclair Radionics Ltd has produced the first calculator that can comfortably fit in the user's pocket along with his wallet and cheque book. Sinclair's Executive is only 3/8in thick, smaller than a pound note, and weighs 2.5 oz, which makes it less than one third the weight and volume of the Rapid Data Rapidman 800. The Executive also has additional functions, including squares, reciprocals, and multiplication or division by a fixed constant.
At £79 [Sterling], the Executive is twice the price of the Rapidman 800. But Clive Sinclair argues that the "executive toy" market is not particularly price sensitive; the firm has ordered components for 100,000 calculators.
Sinclair's "Executive" uses a single metal oxide semiconductor (MOS) chip containing 7000 transistors. This type of integrated circuit normally consumes 350 milliwatts of power, provided by a fairly bulky rechargeable battery. Sinclair's miniaturisation trick depends on a special circuit which reduces the power requirement to about 20 milliwatts. This is accomplished by the elimination of all resisitors from the circuitry and with a clock that turns off the power most of the time. Three small deaf-aid mercury cells provide 20 hours of life - over four months normal usage.
Power is turned on only in 1.7 microsecond pulses, a figure determined by the storage time of a control transistor. The unit has an oscillator clock which operates at 200 kilohertz during calculations and drops to 15 kilohertz between each operation. Thus shut off time ranges from 3.3 microseconds during calculations to over 65 microseconds between. The device relies on the capacitance of the chips to store information during the shut off times, and 1.7 micorseconds is long enough for the chip to carry out a single change of state of the electronics. Any calculation can be done in 1000 such changes."

Clive Sinclair was already well known for his compact and innovative electronics. This demonstrated his flair with an incredible calculator design for this time.

Vintage Calculators

© Text & photographs copyright Nigel Tout  2000-2008 except where noted otherwise.