Air Ministry parallel rule, 1940

By Harper & Tunstall Ltd.  1940 dated.  'Capt. Field's Improved' boxwood parallel rule with brass fittings.  Approximately 45cm/18" in length x 7.5cm/3" wide when closed.  Clear Air Ministry and crown markings.  Some scratches and relatively minor 'bumps' around the edges, the largest photographed.  Good + used condition overall.  As used by the Navigator for route plotting in bomber aircraft.  Unusual manufacturer.  Stock code M21886.