An electronic seal stamp and an electronic sheet are used. A thin film has a first surface and a sensing surface. The runner rail has at least one junction at which the suspension device of the panel is steered in a predetermined manner into a direction of movement on the running surface, whereby the truck has only one carrier roller and one guidance roller, and that the guide roller actuates a junction in the form of a switchable switch which has a pivoting running surface for the carrier roller. The monitoring act includes monitoring a power of the motor, and determining whether the monitored power indicates an undesired flow of fluid through the pump.