Mercury sphygmomanometer is used Koch sound method, electronic sphygmomanometer using the oscillometric method, Koch tone method is through the doctor with a stethoscope to listen to the sound of blood flow in the blood vessel, oscillometric method is by measuring the vibration generated when the blood flow to the vascular wall; although the measuring principle is different, but the test the results from the theory is the same.
In fact, due to the different speed of each doctor's hearing, the sometimes the blood pressure readings are not recorded immediately, but the errors are greater. As a result, each doctor's measurements also produce errors, while electronic blood pressure gauges line up differences between people, and doctors often omit errors and take integers. For example: 128mmHg, 131mmHg, doctors are read as 130mmHg. And electronic sphygmomanometer is what value is measured to show what value, and the user reflects, when measuring at home is always low, go to the hospital to measure blood pressure is high, this is called white dress hypertension.
That is to say in the hospital before the doctor will imperceptibly produce a certain degree of anxiety, tension and mental stress, resulting in increased blood pressure, and in comparison to Songhua River, the amount of blood pressure is low, this is the true reflection of human blood pressure.