This was the first clear demonstration of the physical force of circulation or the blood pressure. Another 100 years later, various devices to measure the blood pressure in experimental conditions and then in clinical situations were devised. In 1894, Riva Rocci devised the present mercury manometer. In this instrument BP is measured in terms of millimetres of mercury. Now we have all kinds of devices, including the spring based dials and electronic devices of all shades which the patient himself can use.
Instruments are now available for continuous recording of blood pressure of a patient when required.
It has not been easy for the epidemiologists and the physicians to define what high blood pressure is. As mentioned earlier, normally it starts increasing from the very birth and reaches the adult level somewhere in midteens. The studies over the last few decades have shown that that is not true and that the blood pressure beyond certain range is harmful at any age. The definition of the blood pressure in an adult at present is 140 mmHg systolic and 90 mmHg as the diastolic. Of course, this will be lower in children depending upon the age.