Abstract: Disclosed is an improved arrangement for allowing more accurate automatic calibration for a system in which blood pressure pulses are derived for remote sites from a calibrated measurement and a waveform measurement, when these are made at different sites. Where a calibrated measurement is made, say, at the brachial artery (11), and a waveform recorded at the radial artery (12), a waveform is derived for the calibrated site using a known transfer function, this drived waveform is then calibrated by the measurements already made, and the calibrated waveform for any remote site, for example the ascending aorta (14), can be derived using a known transfer function.