Incredibly rare counter as used in RAF Filter and Sector Operations Rooms during the Battle of Britain and beyond to display important information relating to raids. On the plotting table within the Operations Room, units of fighter aircraft ordered on patrol, or to intercept, were displayed using special fighter symbols, usually a disc, diamond or irregular hexagon fixed on a metal rod with a stable base. The symbols were moved to correspond with the actual plan positions of the fighters. Heights above sea level were shown using a 'Height Clip' attached to the metal rod. This height clip is manufactured in some form of early plastic and is engraved with the number '11', although only the first '1' has been infilled with paint. A small spring clip is attached via a single screw. Approximately 3 x 3cm. Good condition with some corrosion on the clip. Extremely rare. Stock code M25333-23.