For the planning of a hydropower plant, it is necessary to measure the flow rate and the head difference. Flow measurements can be carried out with water vessels, openings such as sluices, with calibrated measuring weirs, flumes, with the salt dilution measurement method, the hydrometric flow meter, by measuring the velocity with a float, or rising air bubbles. These methods are briefly described. Another method is to determine the discharge from a precipitation area. Since a comprehensive description of all methods would require a separate book, reference is made to the relevant specialist literature. If the performance of a hydraulic machine such as a waterwheel is also to be determined it is necessary to measure the speed, the torque with dynamometers and the electrical power if a generator is used in the drive system. The mechanical brake test rig (Prony Brake) was frequently used in the past to measure the torque. The Prony-brake is therefore described in more detail.