Abstract: The exactness of surge-limit information facilitates the determination of how safely a turbocompressor can operate as well as determining the size of the operational envelope in which a compressor can function with a closed antisurge valve. Furthermore, in order to accurately describe the complete interface between stable and unstable operation, a sufficient number of test points must be found. Consequently, if a turbocompressor operates within the broad ranges of rotational speed or guide vane position or both of them, the unit must be repeatedly tested using different values of process variables; as a result, each test leads the turbocompressor into surge which can be detrimental because of strong dynamic loading. For that reason, this invention describes a technique employed during turbocompressor testing (either without generating surge or with a minimum number of surges) for defining both the shape and the location of a turbocompressor's surge limit.