Bowl-Green painted aluminium, filler plug at side, expansion chamber at base (consists of a plastic expanding bottom). A lead balancing ring is fitted around base of bowl. Inside of bowl painted white with a black painted lubber line carried on a metal strip secured to side of bowl. At centre of verge glass there is a spigot for an alidade. Edge of verge ring graduated to 360 degs. Mounted in a green painted aluminium gimbal ring, 11.25" (28.5cm) dia.
Card-Dia.6.25" (16cm) white plastic (?) with black markings, graduated to 360 degs. Attached to white plastic (?) float at centre.