Extreme of corner averaging means that the extreme value from all the corners of an element are extracted and the value is shown at the centroid of the element.  The tensor and vector components are extracted and the invariants are computed for each corner prior to assigning to the element centroid.  For result components, the corresponding components from each corner is extracted and then the extreme value is assigned to the element centroid.  For invariants, the corresponding invariants are calculated from each tensor at the element corners and then the extreme value is assigned at the centroid.

For example, as shown in Nodal Averaging of Elemental Results, there are four tensors at each corner of the element A:  [A1], [A2], [A3], and [A4].

The extreme of corner aggregation of the xx component at Element A centroid is:

This averaging option is only available when the Use corner data option is checked in the Contour or Iso panels.