By Aston & Mander & Co., London. 1941 dated. 'Capt. Field's Improved' boxwood parallel rule with brass fittings. Approximately 45cm in length x 6.8cm wide when closed. Clear Air Ministry and crown markings. It has been fitted with a brass locking bar. The rule has a few small edge bumbs and light scratches but in good overall condition. As used by the Navigator for route plotting in bomber aircraft. Stock code M22746.