The first experimental model of a liquid aperiodic compass designed and patented by Lieutenant Commander Colin Campbell, RN, and Dr G T Bennett, FRS, in 1918. This model was made up at the Compass Observatory from an old Pattern 200 compass and was tried in the air with satisfactory results.

The magnet system has six small needles mounted in a light frame, which carries four radial wires, the North half painted red and the South half blue. The verge of the compass is fitted with a paper ring graduated to 360° anti-clockwise. The rotating ring carries a pointer by which any desired course can be set. It also carries two parallel wires painted red and blue, on an adjustable slide.

To use the compass the ring is turned until the pointer indicates the course required, then the machine is turned until the North-South pointer on the magnet system is parallel to the two setting wires, care being taken to keep the wires and pointer red to red and vice versa.

If the compass is to be placed to one side of the pilot, the setting wires can be adjusted so that they lie directly between the eye and the centre of the magnet system.

Bowl: Brass painted black. White on inside. Glazed with white radius. Held in holder by four spring mountings. Liquid has dried up.
Bowl holder: Thin brass holder with attachments for ring or cover. Holes in bottom for securing to deck.
Verge ring: Verge ring holds movable parallel wires painted blue and red. Also has lubber spikes.
Card: Consists of four arms, two with arrow heads, only.
Needle: Six very small needles slung beneath card.
Pivot; Stalk and cup. spike on card fits into cup. Inverted cup attached to glass stops card coming off.
O.A. height 4" (10.1cm)