Discrepancy between field minimum/maximum and evaluation of a field quantity at a point in the same location.
When evaluating field minimum/maximum in the fields calculator, Maxwell utilizes first smooth-function, and then evaluates the location and value of the field maximum/minimum. Creating a point in the same position and evaluating fields at the point will lead into a different results, because smooth-function is used. This is a numerical error and decreases as the mesh is improved.