The instrument for measuring blood pressure is called a sphygmomanometer. Sphygmomanometers can be divided into two types: direct and indirect. The working principles of these two types of blood pressure monitors are different. The direct type uses a pressure sensor to directly measure pressure changes, while the principle of the indirect type is to control the pressure applied externally to the measured area, and judge the information on the generation and disappearance of Korotkoff sounds related to the control results. The former can continuously test both arteries and veins, whereas the latter can only measure the systolic and diastolic pressures of arteries.