Bowl- Aluminium, painted grey, filler plug at side. At base of bowl are fitted two expansion chambers, a glass aperture to permit projection of card image onto screen, three legs and two frames to take corrector magnet strips. Two brackets are mounted above verge glass to take corrector magnets. Inside of bowl fited with inner skin (black) and a fitting on aft side permits air bubbles to be removed by tilting bowl and allowingthem to run up between the two skins. A metal lubber pointer is fitted which can be moved against a graduated scale by a knob working through a gland on the fore side of bowl. Mounted in aluminium gimbal ring 10.75" (27.3cm) diameter.
Card- Metal, with a heavy float. Markings are perforations graduated to 360 degs.
Needle-Four flat needles in metal cases mounted below card.