In order to ensure good indoor air quality, sufficient air volume flows in accordance with the design and planning data of the ventilation system are particularly important. Therefore a regular measurement and control (flow measurement) is necessary. There are different measuring methods for volume flow measurement of ventilation systems at air outlets. Frequently used methods are loop measurement, differential pressure measurement and funnel measurement. Which flow measurement method is used to determine the volume flow of air diffusers depends on the installation situation and the shape and accessibility of the air outlets.