Heart Rate Sensor on LEM T

The heart rate sensor on the LEMFO LEM T shows less than on another smartwatch (Huawei Watch GT2e) or on the Xiaomi S1 bracelet.

LEM T 110 bpm
GT2e 134 bpm
S1 130 bpm

The heat rate sensor watch app shows also less.

I use MyRunningApp or HeartOnTop.

Any Solution?

Some members have reported better results when the arm is shaved. But even then it will not give precise results.