Bowl-Diameter 5.3" (13.5cm) sealed white metal unit mounted in aluminium gimbals in an aluminium outer casing diameter 7.72 (19.5cm). From ACO catalogue: the two flat needles are double-pivoted and swing between two flat copper plates so that eddy-current damping is obtained. The top pivot carries an air valve which controlled a gyroscope, the gyroscope actually steering the flying bomb.