A test device for filter systems comprising at least two test units, a management unit for managing and controlling the at least two test units, and signal links via a bi-directional or multi-directional network between the management unit and the at least two test units, particularly for transmitting test program instructions and test results. The club fixture device includes a housing, an insert, and a locking mechanism. The animation is displayed on the screen of a computer monitor together with a live video image of the user’s hands on a musical keyboard. A method for coupling several machine assemblies. The radio propagation characteristics of each section characterize a radio channel of the Wi-Fi access point, and the characterization can be used in a location algorithm. The magnitude of the differential signal output from the circuit can thus sustain in a predetermined range even if the magnitude of the supply voltage is lower than the minimum magnitude required by the conventional circuit.