Sinclair Scientific

The Sinclair Scientific calculator was a 12-function, pocket-sized calculator, sold by Sinclair Radionics for about $100 in the USA and around £45 in the UK.

The Sinclair Scientific first appeared in a case derived from that of the Sinclair Cambridge, but it was not part of the same range. At the time it was launched, in August 1975, it was a highly unusual calculator. It displays only in scientific notation - 5 digit mantissa, 2 digit exponent. Because of the way its processor (a custom chip from Texas Instruments) is designed, it relies on reverse Polish notation (RPN). This unusual method of mathematical problem solving meant that, for instance, to add 2 and 4, one had to enter 2, then 4, then the + symbol. There was no = key. The Scientific Programmable was an advanced version launched in 1977, again using reverse Polish notation. It could handle programs of up to 24 steps and cost £29.95. It used four AAA batteries.

The Scientific Programmable Mark 2 was powered either by a 9V battery or a mains adaptor and cost £17.22. It came with twelve sample programs, with another 294 contained in an additional four-volume library which could be bought for £4.95. Each volume was dedicated to a different application: finance and statistics, mathematics, physics and engineering, and electronics. It also used RPN.

An ingenious aspect of the design which showed Sinclair's inventiveness was that the machine made use of what was originally a 4-function calculator chip. Sinclair realised that by using RPN and allowing a reduced precision of 4 or 5 significant figures displayed in scientific notation, the algorithms for scientific functions could be redesigned and compacted to fit in the same programmable space on the chip. This allowed Sinclair to adapt the relatively low-cost processor and produce an 'electronic slide rule' that fitted easily in a shirt pocket, at a price that even impecunious students could afford.

As a consequence of the compacted logical design and in common with many ground-breaking inventions, operation was a little idiosyncratic, but amazingly flexible with familiarity. Keys trebled up on functionality, important constants were printed on the case below the display, and the instruction book contained many useful keystroke sequences for common functions that were otherwise absent from the device - thus making the calculator much more versatile than the keyboard at first suggests. The log/antilog functions used natural logs and the trignometric functions used radians. The constants printed on the case were useful when converting between radians and degrees, and between log base 10 and log base e.