The Sector Clock was a fundamental part of Ground-controlled interception in England during WW II, especially during the Battle of Britain. The clock face is marked with five-minute red, yellow and blue triangular segments. It has an outer 12-hour ring and an inner 24-hour dial.
Aircraft position was recorded along with the color of the triangle beneath the minute hand at the time of sighting. This was reported to sector headquarters, where counters of the relayed color were used to represent each air raid on a large table with a map of the UK overlaid with a British Modified Grid. As the plots of the raiding aircraft moved, the counters were pushed across the map by magnetic rakes. This system enabled Fighter Controllers to see very quickly where each formation was heading and allowed an estimate to be made of possible targets. The age of the information was readily apparent from the color of the counter. Because of the simplicity of the system, decisions could be made quickly and easily.
Stamped steel case with antique brass lacquered finish for use onshore. Snap in polystyrene lens. Dial diameter: 10.6". Weight: 1.75 lbs. One "AA" battery required (High quality Alkaline battery recommended for best performance). One year manufacturers warranty. Made in Canada with U.S. made movement.