The invention relates to a system comprising a plurality of medical devices, preferably dialysis devices, which are connected to a common supply system, wherein the system has an evaluation unit which is connected to all devices of the system and which is configured such that values set in the different devices and/or predefined values and/or measured values, which are determined by means of at least one sensor and which relate to corresponding parameters, are compared with at least one expected value for recognizing errors of the supply system and/or of an individual device.