Checking the angular accuracy of precision fire-control radar

Precision anti-aircraft fire-control radar equipment may be regarded as the electrical equivalent of an optical instrument such as a theodolite, and it needs similar careful adjustment before use. In this paper the sources of possible instrumental error in determining the angular coordinates of a target are described. The principal sources are incorrect alignment of the mechanical axis of the aerial system, incorrect alignment of the electrical axis of the radar equipment, and incorrect installation with respect to predictor, guns, etc. A description is given of methods of checking and correcting the mechanical accuracy of the instrument in the field, two systems of aligning the electrical axis in the factory, and a method of providing a ¿dummy aircraft¿ in the shape of a balloon-borne target. The paper is confined to Army equipment, and figures are given for the instrumental angular accuracy of the GL3 equipment, this being taken as a representative sample.