In this final panel we give examples of pairs of Sc galaxies that have either similar appearances but greatly different absolute magnitudes or dissimilar appearances where the more chaotic of the pair has the brighter absolute magnitude. Both types of comparisons show again that luminosity class is not primarily a measure of absolute magnitude.
The first comparison is NGC 2276 (MBT0, i = -22m.09; ScII-III) at the upper left with NGC 3294 (MBT0, i = -19m.79; ScI.3) at the upper right. The arm pattern of NGC 3294 is more regular than that in NGC 2276, yet the two galaxies differ by MBT0, i = 2.3 mag, with NGC 2276 being the brighter.
The middle comparison is NGC 3646 (MBT0, i = -23m.13; SbcII) with NGC 6699 (MBT0, i = -21m.92; SbcI.2). NGC 6699 is by far the more regular. The arms are well formed and are hardly fragmented, yet this galaxy is 1.2 mag fainter than the more chaotic NGC 3646 on the left. Although the broken arm pattern of NGC 3646 could possibly be due to tidal interaction with the small faint SBa galaxy NGC 3649 8 arc min away, this seems unlikely, as the projected distance is already 200 kpc and the companion is at least 3 mag fainter. (The redshift of NGC 3649 is unknown.)
The bottom comparison is NGC 1087 (MBT0, i = -21m.43; ScIII.3) with IC 749 (MBT0, i = -18m.65; SBcII-III). The latter is more regular by far than NGC 1087, yet it is 2.8 mag fainter. Furthermore, the very obvious later luminosity class of NGC 1087 makes its very bright luminosity of -21m.43 even more surprising.