A WW2 RAF Air MInistry parallel ruler. Marked 'Captain Field's Improved Parallel', it would have been used by RAF naviagtors and aircrew. It was made by Aston & Mander of London, who supplied navigational and other instruments to the British armed forces in both world wars.
Captain Field's Improved Parallel Rule: The parallel ruler was invented around 1584 by Fabrizio Mordente, but it was not in common use until the 18th century. In the 19th century, Captain William Andrew Field (1796 – 1871) improved the traditional design of parallel ruler by adding a protractor style scale to the upper edge of one rule, and compass points to the opposing edge, which made reading bearings easier. These rulers were made of boxwood, ebony or ivory, and the instrument usually had two brass links.
Aston & Mander: were established in London in 1779 at Old Compton St, Soho. They were manufacturers, wholesalers and exporters of mathematical drawing, surveying and scientific instruments. they specialised in tailors' squares, mathematical scales, rules, tailors' and cloth merchants' tools; anthropological and height measuring instruments, and scholastic geometrical sets and appliances.
The ruler is in good original condition and full working order. There is some minor wear to the original brass finish of the hinges.