Aperiodic compass
Bowl: Brass, painted grey. Filler plug attached to side, expansion chamber fitted to base, an aperture is provided to illuminate spider (blocked off). Mounted in anti-vibration frame incorporating four leaf springs and four location struts. Interior of bowl painted white, fitted with a short black wire lubber line. Rotatable verge ring, N point marked with red triangle and graduated to 1-36 (360 degrees), carries four parallel wires for grid steering. Fitted with two locking devices, to prevent verge ring being turned accidentally.
Card: Wire spider of eight elements. North point marked with letter N and wings in red, S E and W marked in black.
Needle: Six needle magnets slung below spider.
Pivot: Of inverted type, unsighted, presumably having pivot pin on underside of float which engages in pivot cap carried on stem which is attached to base of bowl by a curved disc.
O.A height 4.75" (12cm)