Bowl-Brass with push-on brass lid. Fitted with mounting which could accommodate azimuth sight vane. Fitted with card stop mechanism operating on rim of card by means of brass knob projecting through bowl on fore side. Inside of bowl painted white. Three lubber lines are etched on inside of bowl, a fourth is engraved on card stop bar. Two cros threads are stretched across top of bowl under glass.
Card-Paper covered mica (?), black lettering on white background. Graduated to 32 points and quadrantally in degrees. Jewelled pivot cap at centre of card.