meter does not need a patient-specific calibration. The TDTD method uses Doppler ultrasound to translate the pressure balance principle of blood pressure measurement with a sphygmomanometer to the measurement of ICP. The ophthalmic artery (OA), a unique vessel with intracranial and extracranial segments, is used as a pressure sensor and as a natural pair of scales for absolute ICP value in mmHg or mmH2O measurement. Blood flow in the intracranial OA segment is affected by intracranial pressure, while flow in the extracranial (intraorbital) OA segment is influenced by the externally applied pressure (Pe) to the eyeball and orbital tissues. As with a sphygmomanometer, a special pressure cuff is used - in this case, to compress the tissues surrounding the eyeball and also intraorbital tissues surrounding the extracranial segment of OA. External pressure changes the characteristics of blood flowing from inside the skull cavity into the eye socket. In place of the stethoscope, a Doppler ultrasound beam measures the blood flow pulsations in intracranial and extracranial segments of the ophthalmic artery. The non-invasive ICP meter based on this method gradually increases the pressure over the eyeball and intraorbital tissues so that the blood flow pulsation parameters in two sections of the OA are equal. At this pressure balance point, the applied external pressure (Pe) equals the intracranial pressure (ICP). This measurement method eliminates the main limiting problem of all other non-successful approaches to non-invasive ICP measurement, primarily the individual patient calibration problem. Direct comparison of arterial blood pressure (ABP) and externally applied pressure is the basic arterial blood pressure measurement principle, which eliminates the need for individual calibration. The same calibration-free fundamental principle is used in the TDTD non-invasive ICP absolute value measurement method. The mean value of OA blood flow, its systolic and diastolic values, pulsatility and other indexes are almost the same in both OA segments in the point of balance when ICP equals Pe. As a result of that, all individual influential factors (ABP, cerebrovascular auto-regulation impairment, individual pathophysiological state of patience, individual diameter, and anatomy of OA, hydrodynamic resistance of eyeball vessels, etc.) do not influence the balance of ICP equaling Pe and, as a consequence, such natural “scales” do not need calibration. Ragauskas A. et al. have already published the statistically significant results of a prospective clinical study on assessment of the accuracy and precision of proposed non-invasive absolute ICP value measurement method. The study shows