DescriptionAlso referred to by radar technicians as the PPI, or Plan Position Indicator, this unit displayed what the radar was “seeing.” The unit assisted technicians during regularly scheduled maintenance every few weeks or when the radar reported malfunctions to Ft. Custer, near Battle Creek. Azimuth is the direction to a “target” — an aircraft detected by the radar — and range is the distance. The handwritten note masking-taped to the fold-down counter lists the azimuth and range to permanent echoes [PE] of large fixed objects — such as dunes, hills or smoke stacks — which the radar consistently observed. Technicians used this information to calibrate the radar and verify its accuracy.