The method of calibrating includes selecting discrete levels of cuff pressure and placing the artery under study at those discrete levels of induced pressure with a closed pneumatic cuff system, substantially continually sensing cuff pressures at each discrete level and thereby sensing blood volume change through the artery, electronically determining when a certain number of representative blood volume change signals are substantially equivalent, changing the volume in the closed pneumatic system at each discrete cuff pressure by a predetermined volumetric amount after determining substantial equivalency, and, correcting the blood volume change signal based upon the signals detected during the volume change of the closed pneumatic cuff system. The calibration device includes, in one embodiment, a controllable pneumatic pump, a pressure sensor, a computerized device for determining when a representative number of blood volume change signals (based on the pressure sensor signals) are substantially similar and thereafter generating a calibration trigger signal. The calibration system also includes a device which changes the volume in the closed pneumatic system by a predetermined calibrated volumetric amount upon application of the calibration trigger signal. This volume changing device may be a reciprocating piston.
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