In order to monitor an imaging device for x-ray machines it is proposed that reference system data (19) be recorded in conjunction with a calibration (16) or offset acquisition and that current comparison system data (20) be recorded later in the operating process, and that the performance of a new calibration (16) or the recording of a new offset image be triggered if the current comparison system data (20) deviates from the reference system data (19) by a predefined amount.