Clamp meter readings
To measure 16 A AC you'll select the 20 A AC range. The UT210E manual say ±2.5% + 5 on the 100 A range but doesn't specify for the 20 A range. This implies that on top of the ±2.5 A accuracy on on the 100 A range that there could be an error of 5 on the least significant digit.
The fact that it is capable of measuring DC suggests that it is using a Hall effect sensor for the AC measurements rather than a current transformer. This may be sensitive to the conductor placement.
The user manual says:

Open clamp head, hook electric wire, place electric wire on geometric center indicated by clamp head, make sure the left and right clamp heads are totally closed. There is no gap between the left and right clamp heads.


Figure 1. The geometric center indicators?