A dialyser has assigned thereto a measuring unit that transmits data to the dialyser via a wireless link, the measuring unit being able to determine and transmit to the dialyser at least one measurable variable which can also be determined by another measuring device that is connected physically to the dialyser, a comparison of the at least one measurable variable as determined by the measuring unit and by the measuring device indicating whether the measuring unit is indeed the one assigned to the dialyser in question and/or whether the measuring unit is working properly.
