To compare two items on a list panel of historical versions of a resource definition (displayed by line action H), type CM next to each item, and then press Enter. You can compare the current version with any historical version, or compare any two historical versions.
To compare the before and after images of a change (under primary menu option 4.3 CICS changes), enter S next to the change. The after image appears on the left, the before image on the right.
For more information on these side-by-side comparisons, see Comparing two objects side-by-side.