In order to simplify display and modification of parameters of a measuring device and make them uniform for different measuring devices, it is proposed to transfer from a memory on the measuring device to the operating unit, in addition to parameter values, representational data that defines the presentation of the parameter values on operating unit. Each of the multiple pumps may be operated with a variable speed drive. The processing means is operable in either a first mode, in which the deposited media type is known, or in a second mode, in which the deposited media type is not known. Thus, an output of the subtractor provides a read sensor signal without the interference signal.