Abstract: A blood pressure measuring device is disclosed which uses an inflatable cuff to apply external pressure to a patient's body member. The device detects and measures amplitude of pressure oscillations induced in the cuff by blood flow in the body member as the cuff pressure is decreased in steps from a magnitude above the expected systolic pressure to a magnitude below the expected diastolic blood pressure. The means arterial blood pressure is measured at the step at which the pressure oscillations reach a maximum. Systolic blood pressure is determined by making a first linear approximation to a plurality of amplitude measurements occurring below the expected systolic pressure and making a second linear approximation to a plurality of points occurring above the expected systolic pressure. The systolic pressure is calculated by setting the two approximations equal.