The Fuller calculator, sometimes called Fuller's cylindrical slide rule, is a cylindrical slide rule with a helical main scale taking 50 turns around the cylinder. 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. Like other slide rules, the Fuller is limited to calculations based on multiplication and division with additional scales allowing for trigonometrical 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. Even these advanced machines could not perform trigonometry or exponentiation and they were bigger, heavier and much more expensive than the Fuller. In the mid-twentieth century the handheld Curta mechanical calculator became available which also competed in convenience and price. However, for scientific calculations the Fuller remained viable until 1973 when it was made obsolete by the HP-35 handheld scientific electronic calculator.
Design
Model 1, the standard model
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. The following details describe the version made between 1921 and 1935. There is a papier-mâché cylinder (marked D in the annotated photograph) some 30 centimetres (12 inches) long and 6.2 centimetres (2.4 in) in diameter fastened to a mahogany handle. A second papier-mâché cylinder (marked C) – 16.3 centimetres (6.4 in) long and 8.1 centimetres (3.2 in) diameter – is a slide fit over the first. Both cylinders are covered in paper varnished with shellac. The second, outer, cylinder is printed with the slide rule's primary logarithmic scale in the form of a 50-turn helix 12.70 metres; 500 inches (41 ft 8 in) long with annotations on the scale going from 100 to 1000. A brass tube with a mahogany cap at the top is a slide fit into the first cylinder. A brass pointer with an engraved index marker at its tip (marked A) is attached to the handle so that it points to a place on the primary logarithmic scale, depending on the position to which the scale on cylinder C has been adjusted. A second brass pointer (marked B) is attached to the top cap pointing down over the logarithmic scale and it is positioned by rotating and sliding the cap at the top. This pointer has four index marks (marked B1, B2, B3, B4) such that whichever one is convenient may be used. Printed on the inner cylinder D are simply tables of data for reference purposes.
The calculator was sold in a hinged mahogany case 46 by 12 by 11 centimetres (18.1 in × 4.7 in × 4.3 in) which, if required, holds the instrument when in use by means a brass support that can be latched to the outer end of the case. Out of its case the calculator weighs about 900 grams (32 oz). 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.
Other Fuller models The calculator described above was called "Model No. 1" . Model 2 had scales on the inner cylinder for calculating logs and sines. The "Fuller-Bakewell" model 3 had two scales of angles printed on the inner cylinder to calculate cosine² and sine⋅cosine for use by engineers and surveyors for tacheometry calculations. A smaller model with a 5.1 metres (200 in) scale was available for a short time but very few survive. In about 1935 the brass tube was replaced by one of phenolic resin and in about 1945 the mahogany was replaced by Bakelite. Included in Stanley's 1912 catalogue and continuing there until 1958 was Barnard's Coordinate calculator. It is very similar in construction to the Fuller instruments but its pointers have multiple indices so additional trigonometrical functions can be used. It cost slightly less than the Fuller-Bakewell and a 1919 example is held by the Science Museum, London. In 1962 the Whythe-Fuller complex number calculator was introduced. As well as being able to multiply and divide complex numbers it can convert between Cartesian and polar coordinates.
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