When the mi band 4 screen lights up, swipe up to find the heart rate icon.
Keep quiet, click on the heart rate icon and start measuring the heart rate.
When measuring the heart rate, the values on the page will change. At this point, do not move your arm and wait for the measurement to end.
After the measurement, your heart rate will be displayed on the page with a retest icon below. This means that the heart rate measurement has ended.
After clicking, in my state, click the heart rate option again. After the measurement, you can also turn on Xiaomi Exercise and click the option of heart rate to enter. Enter the heart rate viewing interface, and you can view your own heart rate records measured in history.