Factors affects the heart rate measuring
Factors like wearing the watch too loosely, swinging your arms, or sliding of the watch over your skin can impact heart rate readings.
In addition, wearing the watch too tightly, raising your arms, or clenching your fists can affect blood circulation, which also affects sensor performance. When testing your heart rate, it is recommended that you keep your arm straight, remain static, and relax your muscles. Ensure that the watch remains in close contact with your skin.
Note: Even when you wear the watch correctly, individual differences such as skin color, body hair, tattoos, and scars can also affect heart rate sensor performance slightly.