1. The error of the checked pressure gauge always increases or decreases a fixed value.
2. The reading pointer is Jumping or falling back
3. The speed of indication in the checked pressure gauge is different from start scale and last scale,it is also called non-linear error, or curve error.
4. Non-return zero of pointer, return error and overshoot of tapping displacement
5. The indication value is not stable and the pressure decreases obviously.