During the measurement process, an inflatable cuff is used to block the blood flow of the wrist artery. Due to the hemodynamic effects of heart beating, pressure fluctuations synchronized with heart beating, known as pulse waves, will overlap on the cuff pressure. In the traditional blood pressure measurement process, the air pump first inflates the cuff to a pressure slightly higher than the blood pressure, and then slowly presses down the cuff through the slow air leakage valve. During the blood pressure reduction process, pulse wave signals are collected. In the process of pressure rise measurement, the measurement principle is the same as that of pressure drop measurement, except for changing the slow pressure drop process to uniform pressure and collecting pulse wave signals during the pressure process. By selecting an air pump with stable inflation and automatic software algorithm control, the air pressure inside the cuff rises steadily and evenly. During the process of slowly increasing cuff pressure from zero, the pulse wave signal intensity superimposed on it will undergo a process of first reaching zero, then slowly appearing, then becoming strong from weak to maximum, then becoming weak from strong to weak, and finally completely disappearing.

Blood pressure measurement calculates blood pressure based on the relationship between pulse amplitude and cuff pressure. The cuff pressure corresponding to the maximum value of the pulse wave is the average pressure, and the systolic and diastolic pressures are determined based on the ratio of the maximum amplitude of the pulse wave when the pulse intensity decreases and increases. This process is automatically completed by a dedicated chip. Simultaneously, the corresponding pulse value is obtained by calculating the frequency of the pulse wave.

Compared with the step-down measurement method, the step-down measurement method has the following obvious advantages:
1. It avoids measurement errors caused by the nonlinear leakage speed of the pressure reducing mechanical slow leakage valve.
2. The measurement time is shortened, the maximum pressure of the wrist strap is reduced, the accuracy is higher, and the user feels more comfortable.