A plotting intrument for air navigation that orginally consisted of three parts: a circular plastic disc approximately 150mm in diameter with a square grid drawn on it; a circular plastic disc approximately 150mm in diameter, marked in degrees from 0 to 360 by 0.5 degrees around its circumference; and a plastic rule approximately 315mm long marked in inches to 12 by 0.1 (with zero at centre of instrument). The degree disc and the rule are joined to metal rings with a hole at the centre and appear to have been able to rotate independently on top of the grid disc. Near the centre of the middle (degrees) disc is the inscription 'J.H. STEWARD LONDON'. Due to the degradation of the plastic, the instrument is now in many pieces.

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.