Navigator's indicator designed by Lieut C.S. Gill RNR, British Patent No. 347324, published by Marine Instruments Limited, London & Glasgow, Rees, Pitchford & Co,. London. This is an aide memoire for the formulae and other information required for astro-navigation,

The instrument comprises a circular card backing with navigational terms in 24 segments around the periphery e.g. 'Vertical Sextant Angle'. A second card dial, blue in colour, can be rotated against the outer dial and has apertures through which known data can be set and sources of information (manuals etc.) can be read. The rear of the main body has a list of the sources. It has a paper case with a full size illustration of the indicator.

This instrument consists of two moveable cardboard circles one on top of the other. The top one, blue in colour, has windows so that formulae and other data may be read off from the bottom one, which is white in colour.
Diameter of top circle: 9.8" (25 cm)
Diameter of bottom circle: 8.5" (21.5 cm)