The D5h character table lists 2 S53 operations. My background in group theory is (obviously) not the strongest. I would have told my students to list 2 S52 operations, as consistent with the listed 2 C52 operations. Is there a short explanation of why S53 is the prefered notation for the improper rotations? When I first introduce this notation, I tell them that we try to minimize the value of the superscripts, thus, for instance, C3 rather than C62 in D6h. Calling these operations 2 S53 seems to disagree with that approach.