What is the principle of measuring blood pressure? Which is more accurate?

The instrument for measuring blood pressure is called sphygmomanometer. Sphygmomanometer can be divided into direct type and indirect type. At present, there are three kinds of sphygmomanometers on the market, namely traditional mercury sphygmomanometers, barometer (spring) sphygmomanometers, electronic sphygmomanometers and so on. These three sphygmomanometers are indirect measurements. Its working principle is to control the pressure applied to the measured part from the outside and judge the control result and the information of the appearance and disappearance of Coriolis sound. Electronic sphygmomanometer uses electronic pressure and pulsation sensors (instead of stethoscope) to identify pressure and pulsation signals and express them in digital form. The upper part of its screen is systolic blood pressure, and the lower part is diastolic blood pressure and pulse number. The choice of sphygmomanometer depends on the convenience, accuracy and maintainability of use. In principle, it is recommended that you use a mercury sphygmomanometer. Its advantages are high accuracy and reliability of blood pressure measurement. The disadvantage is that it is heavy, mercury may leak, and it is inconvenient to carry. You need to listen with a stethoscope, but people with poor hearing can't use it. The advantages of surface sphygmomanometer are convenient to carry and simple to operate; The disadvantage is that the accuracy of blood pressure measurement is not as good as that of mercury sphygmomanometer, and it is also difficult to maintain, and the number of scales is small, which is difficult for the elderly with poor hearing and vision to use. The electronic sphygmomanometer is light in weight, easy to carry and easy to operate. But sometimes patients use it improperly, and there is an error between the measured blood pressure and the actual blood pressure. It is often necessary to calibrate the standard mercury sphygmomanometer, which is expensive. Other products such as finger sphygmomanometer and wrist sphygmomanometer are not only inaccurate, but also expensive, so it is not recommended to use them.