Consists of a bowl shaped frame hung in gimbals. The centre part of the face of the bowl is recessed, and within this recess a graduated steel plate (graduated quadrantally in degrees) revolves about a centre pin. A narrow ridge seperates the centre recess from another recess about 0.5" wide in which an azimuth circle revolves; this unit carrying sight vanes, dark shades, and a reflecting glass. On the two ridges enclosing the circle, lines are engraved to represent the lubber line, and when taking bearings the centre plate is set to show the ship's head, and the bearings of an object are taken by means of the azimuth circle.