Significant modifications to the algorithms used meant that a chipset intended for a four-function calculator was able to process scientific functions, but at the cost of reduced speed and accuracy.
[3][4] Clive Sinclair wanted to design a calculator to compete with the HP-35 using this series of chips.
Despite scepticism about the feasibility of the project from Texas Instruments engineers, Nigel Searle was able to design algorithms that sacrificed some speed and accuracy in order to implement scientific functions[4] on the TMS0805 variation.
[10] The HP-35 used five chips, and had been developed by twenty engineers at a cost of a million dollars, leading the Texas Instruments engineers to think that Sinclair's aim to build a scientific calculator around the TMS0805 chip, which could barely handle four-function arithmetic, was impossible.
[4][11] However, by sacrificing some speed and accuracy, Sinclair used clever algorithms to run scientific operations on a chip with room for just 320 instructions.
[12] Instead of an "equals" button, the + or − keys are used to enter the initial value of a calculation, followed by subsequent operand(s) each followed by their appropriate operator(s).
[4] The code to normalize and display the computed values is roughly the same in the TI and Sinclair programs.
[4] Ken Shirriff, an employee of Google, reverse engineered a Sinclair Scientific in 2013 and built a simulator using the original algorithms.
[13] The build time was advertised as being around three hours, and required a soldering iron and a pair of cutters.
[16][17] However, included with the calculator was a library of over 120 programs that performed common operations in mathematics, geometry, statistics, finance, physics, electronics, engineering, as well as fluid mechanics and materials science.
The C key performs a clear; pressing it sets the calculator to a state with zero in the internal registers.
The functions available are sine, arcsine, cosine, arccosine, tangent, arctangent, logarithm and antilogarithm.