heh, this is one reason why you want am artist with good color experience to do things like accurate preservation efforts (pinball art...)  ,rather than a person whos not too color savvy, and has little experience with using them.
 Im somewhat shocked at the variances in results though.  I assumed that may be slight differences... but the range of results is quite vast, all over the map.
Edit:  Took the test.  Got a Perfect   

 A little surprised, cause there were a few tones that were really tricky to tell apart.