adiabatic compressible flow at sea level uncorrected for airspeed system errors. [http://www.easa.eu.int/doc/Agency_Mesures/Certification_Spec/decision_ED_2003_11_RM.pdf] Outside of the former Soviet bloc, most airspeed indicators show the speed in knot s i.e. nautical miles per hour. Some light aircraft have airspeed indicators showing speed in miles per hour. An airspeed indicator is a differential pressure