Constant altitude plan position indicator

The constant altitude plan position indicator, better known as CAPPI, is a radar display which gives a horizontal cross-section of data at constant altitude. It has been developed by McGill University in Montreal by the Stormy Weather Group to circumvent some problems with the PPI: In 1954, McGill University obtained a new radar (CPS-9) which had a better resolution and used FASE (Fast Azimuth Slow Elevation) to program multi-angle soundings of the atmosphere.