Rangefinder converters (2), metal / masonite, made by E E & S, England, 1942
A flat rectangular board bounded by a metal edge and having a pair of parallel metal indicators. The board has a semi-circular polar grid laid out on it. It is a graphical device for plotting the position of an aircraft on a map given its bearing (the direction to it from the point of view of an observer), its angle above the horizon and the distance to the aircraft along this slant. It solves the vertical triangle giving the height of the aircraft and its position on the map for anti-aircraft artillery range-finder calculations.
In use it converts polar to linear co-ordinates. A sliding linear scale is graduated 1 - 40, i.e. 1,000 - 40,000 feet; and a logarithmic circular scale shows the radius to 19,000 feet, i.e., marked each 10 degrees from 0 to 5,000 feet, each 5 degrees from 5,000 to 10,000 feet, and each degree from 10,000 feet to 19,000 feet.
Marked EE and S 1942, D and D No. 311 (one of models), 314 (other model).