Test benches are an important tool in industry. In the automotive industry test benches are common in the development and parametrization of the internal combustion engine, of control units, of the drive line up to the entire vehicle. The increased distribution of alternative fuel vehicles leads to a further increased use of test benches. The device under test must be operated at a test bench as it would be operated in a vehicle. In a vehicle, the load to the internal combustion engine results from the environment such as the slope of the road. The load has to be computed and enforced by one or more dynamometer/s at a test bench. If the configuration of the test bench and the test bench controller allow an accurate simultion of the load conditions, measurements in a vehicle can be replaced by measurements at a test bench. The advantages of test benches are reduced costs and time spent as well as reproducible enviroment conditions. The significance of experiments at a test bench is a direct consequence of the precision of the test bench controller. The task of the test bench controller is to set the inputs to the test bench ? the accelerator pedal position of the internal combustion engine and the manipulated variable/s of the dynamometer ? such that the measured shaft torque tracks the desired shaft torque and the measured engine speed tracks the desired engine speed while the tracking error remains within a defined range. Either, an electric dynamometer, a hydrodynamic dynamometer or both dynamometers serve as actuators to the test bench controller. Hydrodynamic dynamometers are an interesting alternative to electric dynamometers as their performance is very high, the moment of inertia is small and the costs are quite low.