ESDU 93020 is ancillary to and is for use in conjunction with ESDU 88025, which provides a definitive method for deriving primary air-data parameters in hypersonic flight with excellent precision, provided an accurate value of static pressure is available. ESDU 93020 provides an accurate means of deriving this static pressure without relying on a static pressure system. It is not possible to evaluate the relationship between the sensed static pressure and the real ambient pressure when the air is calorically and thermally imperfect as it is behind the shock in hypersonic flight. The static pressure is then used in the method of ESDU 88025. ESDU 93020 uses the ratio of static to total pressures behind a normal (detached) shock which is given in terms of quantities tabulated in ESDU 88025 and requires a knowledge of total temperature and pressure. However, it also requires a knowledge of the ambient temperature and the lapse rate, either from meteorological balloons or satellite observation, although an accuracy of 4 or 5 K for ambient temperature will be satisfactory. A worked example illustrates the use of the method for the same flight conditions used in the example in ESDU 88025.