The TCAS computer calculates the altitude separation between own airplane and the target. It uses the barometric altitudes of the airplanes to do this. The altitude separation shows on the ND in hundreds of feet. If the traffic is above, the digits show above the traffic symbol with a plus (+) sign. If the traffic is below, the digits show below the traffic symbol with a minus (-) sign.
If the altitude separation is less than 100 feet, 00 shows.
If the altitude separation cannot be calculated, the altitude
display does not show.