Why is the measurement of SpO2 on the REDMI Watch 5 inaccurate?

If the measurement of SpO₂ on the REDMI Watch 5 is inaccurate, please refer to the following details:
1. It is recommended to wear the REDMI Watch 5 1.5cm-2cm away from the wrist bone;
2. Ensure that the sensing area on the back of the REDMI Watch 5 is in full contact with the skin of your wrist;
3. A dirty sensor area on the back of the watch or sweat between the wrist and the device will affect the measurement results;
4. In a cold environment, the wrist skin temperature will decrease, which in turn leads to a decrease in blood flow and affects the measurement results;
5. Tattoos or pigmentation on the wrist where the watch is worn can affect the penetration of light from the sensor, resulting in inaccurate measurements.