This item is a Manual Navigational Computor (sic), Mark III D, used during WWII and for many years after. Ref No. 6B/180 was for use in aeroplanes and provided a rapid means of solving problems involving the effect of wind on the track and ground speed of an aeroplane. These, together with interception problems, are solved geographically by constructing a vector triangle. A height and airspeed computor (sic), calibrated for the International Commission for Aerial Navigation (ICAN) atmosphere specifies a standard drop in temperature per 1000ft – needed to solve certain problems. Housed in a plastic and metal case with a hinged, metal, cover, this machine would have been worn strapped to the leg of a flyer. The top face hinges up to reveal a true course computer that moves with the help of a dial.
Manual Navigational Computer, Mark III D