Efficient installation of airborne electronic equipment requires adequate data to design a heat removal system for the airplane. For many years aircraft generators have been supplied with rating charts to define their cooling requirements: electronic equipment now requires similar treatment. The form of the chart depends on the nature of the equipment, but consists, essentially, of a nomograph showing required cooling airflow and pressure drop vs air temperature. When pertinent, it should also include such factors as life, output, surrounding wall temperature, etc. Such charts make it convenient to design and compare performance of ram and fan driven cooling systems, and to compare different equipment designs in terms of their flow and pressure drop requirements. Examples of several different types of charts, their preparation and their use, are presented.