Aircraft computer.
Black Bakelite or similar plastic frame holds a metal plate with inset rotatable circular
degree scale with transparent circular window. Against the rotatable circular degree scale is a fixed scale 40 – 0 - 40 marked “Drift Port - Var East - Var West - Drift Starboard”. A knob at the side of the plastic frame drives a conical graticule scale calibrated 40 – 40 beneath this window.

On the reverse side which is labelled “ICAN Calibration” (International Committee for Air Navigation, a standard-setting body) a metal circular slide rule has an outer scale “Miles, an inner rotatable scale marked “Ind AS” (indicated airspeed) “Minutes” and two apertures with scales beneath for Height correction and for Air Speed Correction.

There is a plastic leatherette case which is marked Mk II (sic) 6B/270

The computer solves the navigational vector triangle of airspeed and heading, wind speed and direction, course made good and ground speed, where one of the parameters is unknown.

Rotating dial on reverse for air speed and height corrections. Revolving scale on face. Rotating inner scale. In plastic case for wind and navigation calculator Mk. II. For use in aircraft.