Experience accumulated during the past 10 years in measuring turbojet-engine thrust in altitude facilities is summarized herein to indicate the currently best-known techniques applicable for obtaining in-flight thrust measurements. Problems that are encountered in obtaining accurate thrust measurements are illustrated, and the resultant techniques required for measurement of the net thrust of several typical types of turbojet installations are discussed. Techniques for obtaining a performance calibration of the basic engine while it is installed in an airplane are also indicated.