Fuller calculator

This creates an instrument of considerable precision – it is equivalent to a traditional slide rule 25.40 metres (1,000 inches) long.

It was invented in 1878 by George Fuller, professor of engineering at Queen's University Belfast, and despite its size and price it remained on the market for nearly a century because it outperformed nearly all other slide rules.

As with other slide rules, the Fuller is limited to calculations based on multiplication and division with additional scales allowing for trigonometical and exponential functions.

The mechanical calculators produced in the same era were generally restricted to addition and subtraction with only advanced versions, like the Arithmometer, able to multiply and divide.

In the mid-twentieth century the handheld Curta mechanical calculator became available which also competed in convenience and price.

In essence, the calculator consists of three separate hollow cylindrical parts that can twist and slide over each other about a common axis without any tendency to slip.

[8] For all except the earliest instruments the last two digits of the date and a serial number, believed to be consecutively allocated, are stamped at the top of pointer B.

It is very similar in construction to the Fuller instruments but its pointers have multiple indices so additional trigonometrical functions can be used.

[19] The calculator's unusual single-scale design[note 3] makes its 12.70-metre (500-inch) helical spiral equivalent to a scale twice this length on a traditional slide rule – 25.40 metres (1,000 inches) long.

[23] When it was introduced the Fuller calculator had a much greater precision than other slide rules although the Thacher instrument became available a couple of years later.

[24][25][26][27] However, both of these types of slide rule required some skill to operate accurately compared with mechanical calculators which manipulated exact numerical digits rather than using positioning and reading from a graduated scale.

Mechanical calculators could only add and subtract (which the Fuller did not do at all) although models such as the Arithmometer could perform all four functions of elementary arithmetic.

[26][28][30] However, a revolutionary miniature mechanical calculator went on sale in the mid-twentieth century – while Curt Herzstark had been imprisoned in a Nazi concentration camp in World War II he had developed the design of the handheld Curta mechanical calculator.

[9][45] In 1949 Encyclopædia Britannica, noting that the Fuller had been designed in 1878, reported that it "has been in considerable use up to the present time".

[50][51] But in 1972 Hewlett-Packard introduced the HP-35, the first handheld calculator with scientific functions, at $395 – the Fuller went out of production the next year.

[52][31] The instrument operates on the principle that two pointers are set at an appropriate separation on the helical scale of the calculator.

If the cylinder is then moved without altering the positions of the pointers, this same ratio applies between any other pair of numbers addressed.