Sinclair Cambridge

The Sinclair Cambridge calculator was a 4-function, pocket-sized calculator manufactured by Sinclair Research Ltd.. It sold initially for about £43 ($100). It was introduced in the summer of 1973 and sold in both kit and assembled forms. Power was supplied by four AAA sized alkaline cells.

Later models of the calculator had a primitive kind of exponential notation, which could handle numbers between 1E+80 and 1E-20 - however the screen displayed only 8 mantissa digits and no exponent digits. If the number was larger than 99999999 or smaller than 0.0000001 the decimal point simply vanished from the display, and you had to multiply or divide by powers of ten until the decimal point reappeared in the display to figure out the actual magnitude of the number.

Internally, the full 8-digit mantissa was always stored. And as far as the calculator concerned, the numbers 1E+80 and 1E-20 were equal! If you had entered 1E+79 (which could be computed as e.g. 10000000 * 10000000 * 10000000 * 10000000 * 10000000 * 10000000 * 10000000 * 10000000 * 10000000 * 10000000 * 10000000 * 100), and then multiplied that number by 10, you suddenly had 1E-20. If you instead multiplied 1E+79 by 1E+21, you got 1.0000000 instead of 1E+100. Those models of Sinclair Cambridge could never overflow, the two-digit decimal exponent just "rolled around", and if you kept track of how much it rolled around, you could handle numbers of any size. If you divided by zero with this calculator, it attempted to actually perform the division - which of course caught the calculator in an endless loop, terminated only by pressing the "C" (Clear) button.

External links

* [http://www.vintagecalculators.com/html/cambridge_models.html Vintage Calculators Web Museum]