A course and distance indicator made of cellulose-based plastic with some metal components. It comprises three plastic discs with two nickel plated arms with sliding cursors. All rotate around the centre of the device. The instrument was intended to be used for airborne dead reckoning, and was a simplified version of the Battenberg Course and Distance Indicator, an instrument designed for tactical problems involving vector diagrams. It was later developed as the Course and Distance Calculator, which became a standard instrument in air navigation to the 1930s. In use, the graticule and arms are positioned to represent the triangle of velocities.

This is one of a number of items formerly belonging to Henry Theodore Augustus Bosanquet (1870-1959), who was a leading figure in the development of air navigation in Britain during the First World War.