serves to subtract the second signal supplied by the counter 44 from the primary signal of the counter 28 such that the result is the supplying of a compensated signal more nearly representing the waveform 31 since the secondary sensor 35 is not subject to the arterial pressure changes there is no deletion of the magnitude of that signal but only a deletion of the extraneous signals which are common to both the primary sensor 15 and any secondary transducers 35 the output of subtractor 29 is used by the data processor 30 for calculation and display in fig3 is shown a second embodiment of the invention in which the primary sensor 45 incorporates a fixed plate 46 and a movable plate 47 in this embodiment the plate 45 is mounted on the side of the fixed plate 46 opposite the skin and is actuated by a small rod 48 which extends through a center opening in the plate 46 and contacts a pad 48a on the wrist skin thus the capacitance of this sensor decreases as the pressure in the artery 11 increases which normally causes the skin to expand outward and is sensed through the conductors 49 and 50 connecting to a variable frequency oscillator 51 similarly there are positioned to the side of the primary sensor 45 the secondary sensors 52 and 52b which also supply a signal in the form of a capacitance value to the same variable frequency oscillator through the conductors 54 and 55 parallel connected with the conductors 49 and 50 the output signal from the variable frequency oscillator is fed through the conductor 56 to an and gate 57 receiving a signal through the conductor 58 from a counter 59.