Sinclair_Executive

Sinclair Executive

The Sinclair Executive was Clive Sinclair’s first venture into the pocket calculator market. The Executive was the world’s first “slimline” pocket calculator. It was variously described as “a piece of personal jewelry” (New Scientist) and “at once a conversation piece, a rich man’s plaything and a functional business machine” (Design Magazine). An example of the calculator is displayed at the Museum of Modern Art in New York.

The Executive was launched in August 1972 at the price of £79.95 plus VAT, which at that time was about two or three times the average weekly wage. It weighed only 2.5 ounces (~70 grams) and measured 5.5 × 2.25 × 0.4 inches (14 × 5.7 × 1.0 cm).

The Executive was remarkably thin for its time, made possible by the first use of button-type batteries to power a calculator. To do this, Sinclair had to overcome the problem of the power hungry calculator electronics and LED display. It was common to pulse the power to the LED display to reduce power consumption, but Sinclair's engineers found that it was also possible to rapidly pulse the main calculator integrated circuit (chip). This method of operation relied on the capacitance of the devices in the chip to retain information during a calculation, and it was claimed that the power consumption of the chip was reduced from 350 milliwatts to about 20 milliwatts. Texas Instruments, the manufacturer of the chip, said it had not tested them operating like this, but Sinclair said that it tested all the chips before it used them. Although this had the effect of extending battery life, they still only lasted for a few hours of intermittent use and also had the tendency to explode due to overheating if the calculator was left switched on, damaging the calculator casing.