Why the reading can not be reset when performing AC and DC current measurements through clamp meter?

For AC current measurement:
It is affected by electromagnetic field. The clamp jaw is designed with hall component (a sensitive device), sensitive with magnetism, heat and mechanical stress to some extents. When the clamp meter is interfered by the electromagnetic field in the measurement environment, the reading will be changed or can not be reset.

For DC current measurement:
After measurement of large current, there will be residual magnetism at the clamp jaw for some time, and the least significant digit will be displayed on the LCD. Please long press REL to reset the reading.