The Bygrave slide rule is a

slide rule The slide rule is a mechanical analog computer which is used primarily for multiplication and division, and for functions such as exponents, roots, logarithms, and trigonometry. It is not typically designed for addition or subtraction, which ...

named for its inventor, Captain Leonard Charles Bygrave of the

RAF The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...

. It was used in celestial navigation, primarily in aviation. Officially, it was called the A. M. L. Position Line Slide Rule (A.M.L. for Air Ministry Laboratories). It was developed in 1920 at the Air Ministry Laboratories at Kensington in London and was produced by Henry Hughes & Son Ltd of London until the mid-1930s. It solved the so-called celestial triangle accurately to about one minute of arc and quickly enough for aerial navigation. The solution of the celestial triangle used the

John Napier John Napier of Merchiston (; 1 February 1550 – 4 April 1617), nicknamed Marvellous Merchiston, was a Scottish landowner known as a mathematician, physicist, and astronomer. He was the 8th Laird of Merchiston. His Latinized name was Ioan ...

rules for solution of square-angled spherical triangles. The slide rule was constructed as two coaxial tubes with spiral scales, like the Fuller's cylindrical slide rules, with yet another tube on the outside carrying the cursors. During the Second World War, a closely related version was produced in Germany by Dennert & Pape as the HR1, MHR1 and HR2.

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Sir Francis Chichester Sir Francis Charles Chichester KBE (17 September 1901 – 26 August 1972) was a British businessman, pioneering aviator and solo sailor. He was knighted by Queen Elizabeth II for becoming the first person to sail single-handed around the wor ...

was a renowned aviator and yachtsman. He used a Bygrave Slide Rule as an aid to navigation during flights in the 1930s, one of which was the first solo flight from New Zealand to Australia in a

Gipsy Moth The de Havilland DH.60 Moth is a 1920s British two-seat touring and training aircraft that was developed into a series of aircraft by the de Havilland Aircraft Company. Development The DH.60 was developed from the larger DH.51 biplane ...

biplane. He later completed a round the world cruise in his yacht

Gipsy Moth IV ''Gipsy Moth IV'' is a ketch that Sir Francis Chichester commissioned specifically to sail single-handed around the globe, racing against the times set by the clipper ships of the 19th century. Gipsy Moth IV was the first ever purpose built o ...

. This was the first solo circumnavigation using the

clipper route The clipper route was the traditional route derived from the Brouwer Route and sailed by clipper ships between Europe and the Far East, Australia and New Zealand. The route ran from west to east through the Southern Ocean, to make use of the s ...

. Sir Francis Chichester wrote about these exploits in his autobiography, entitled The Lonely Sea and the Sky.

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* *{{cite web, title=Position Line Slide Rules, author=van Riet, Ronald W.M., url=http://www.rechenschieber.org/PositionLineSlideRules.pdf Navigational equipment Mechanical calculators Logarithms English inventions Analog computers Historical scientific instruments

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