Howard MK II, sun compass.

Information from http://perso.orange.fr/cadrans-solaires/navigation/howard/howard_uk.html
The Instrument consists of:
A Circular Bearing Plate, engraved anti-clockwise in degrees from 0° to 360°. The plate also has an inner circle graduated from 0° to 360° clockwise but this is normally covered by:
A Circular Time Plate,a white plastic disc, which revolves independently on the circular bearing plate. Usually, it has an index line, marked '12' and drawn as a radius from the centre. The index line is used as a 1200 hours (midday) baseline for drawing other lines to represent times of the day. If the index line is not engraved on the plate it can be drawn in with a pencil.
A Slotted Ruler, pivoting on the centre of the circular bearing plate to form a radius. When clamped down it holds the circular time plate (plastic disc) in position.
Spirit Level. In some models the spirit level is incorporated in the pointer, on the opposite side of the gnomon to the slotted ruler, as shown in the illustrations. In other models it is fitted on the outside edge of the bearing plate.
A Gnomon, mounted vertically in the centre of the circular bearing plate around which the slotted ruler and time plate can revolve.
Mountings. The instrument can be mounted on a vehicle or hand held. Its box, which contains spare gnomons, may be screwed on to the vehicle for better security.