This part of ISO 4392 describes a method of determining the low-speed characteristics of positive-displacement rotary fluid power motors under constant flow and constant torque conditions. Motors may be of either the fixed or variable-displacement type. The method involves testing at slow speeds, which may generate frequencies having a significant influence upon the steady continuous torque output of the motor and affect the system to which the motor would be connected. The accuracy of measurement is divided into three classes, А, В and C, which are explained in annex A.