Hi Dave,
Who knows!
I think he might be confusing a colorimeter & a gray card?
Also - just for the record - adjusting colours "by eye" is probably the least accurate method. I'm reminded of a test I did with a collegue on just this point ...
We took a couple of shots of me - one holding a WhiBal card, one without. I put the one without the card up on the screen in ACR - moved the temp and tint sliders and asked my friend to put them where the skin tones looked best (he shoots weddings, so I'd expect him to be good at skin tones). When he had it looking (what he thought was) right we flicked to the one with the WhiBal card and used the whitebalance tool ...
... from this we learned two things ...
1. That although he was in the "ball park", he wasn't particularly close, and
2. We agreed that the changes made by using the white balance tool were much closer.
So for colour critical shots (like portraiture) I ALWAYS go off the WhiBal card and seldom make anything but the smallest of changes from there.