 The altitude of the aircraft (in the example, 2,500 ft.) is compared to the altitude of the PCAS altitude (e.g., 1,500 ft.) and the relative altitude is calculated (e.g., 1,000 ft. above you).With relative direction, altitude and range determined, XRX displays this information and stores it in memory.If additional aircraft are within detection range, the above process is repeated for each aircraft.