I've read Tom Graves years ago - and have forgotten his line of reasoning. The body inch is dependent on the distance between two joints on the first finger, it's true, which may be why the MI is sometimes given as .814 and sometimes .816. It really doesn't matter that much - we're talking Rock Art not a contact breaker gap. Thom supported this measurement and, if you follow his line of reasoning, it does open up some understanding of cup and ring art. Then, if you extend it further, it makes it more likely that his Megalithic Yard was a full pace and that the inherent variability of the unit, much greater than in the inch, makes it a statistical uncertainty to modern measuring systems. "If I could turn back t--ime!"