The measuring site shall be a level area free from appreciable wave-reflecting surfaces within an ellipse having a major axis of 20 m and a minor axis of 17 73 m. The antenna and the centre of the engine must be located on the major axis of the ellipse, the plane of symmetry of the tractor being parallel to the minor axis. The antenna and the point of intersection of the side of the engine nearest to the antenna with the major axis must each be located at a focal point of the ellipse.
