Devices, systems, and methods for calibrating blood pressure substitution for monitoring blood pressure of subject

The present invention relates to a device, system and method for calibrating a blood pressure BP substitution for use in monitoring the blood pressure of a subject. The apparatus comprises a BP input (51), a sensor input (52) and a processing unit (53) configured to determine whether the cuff is inflated using a first characteristic in a first time-dependent sensor signal and a second characteristic in a second time-dependent sensor signal during inflation of the cuff. Calculating a pulse correlation value according to the first time correlation sensor signal and the second time correlation sensor signal, wherein the pulse correlation value is a pulse arrival time (PAT) value or a pulse transmission time (PTT) value; pairs of pulse-related values and corresponding cuff pressure values are selected to calculate calibration parameters for BP substitution, one pair comprising pulse-related values and corresponding time-related cuff pressure values, where only pairs of pulse-related values and corresponding cuff