Abstract: Method for determining, monitoring and updating correction data for correcting measured value distortions and for calibrating liquid-filled transmission systems, via which signals from the patient detected in the body of a patient are transmitted to an external measured value receiver, in particular for invasive pressure measurements in cardiology, intensive care medicine and anaesthesia. The correction data are determined in the frequency range for each frequency from statistics of the signals from the patient measured at this frequency, in particular from the transmission function obtained from the signal from the patient. In the determination of the correction data, empirically checked assumptions about the corresponding statistics of undistorted signals from the patient and general properties of the transmission function are used.