About Comparing Defined Compare Areas
You can define the compare areas for the comparison of two PCB viewables or of two schematic viewables of the same design. Define one or more rectangular areas to compare. The compare areas are shown in all views of both designs, and the compare areas cannot overlap. Only elements within the defined compare area and objects whose bounds intersect the area boundaries are compared. You cannot edit a defined compare area. Instead, delete it and define a new one.