So they eventually match it up with a tree they can actually date? Seems like a lot of error might be able to creep in with this methodology. “Wiggle matching” seems like an art form.
It has to do with the sequence of dates for the individual rings — they’ll be in the same order, that’s why the overlap works.
amusing aside:
http://www.freerepublic.com/focus/chat/1563039/posts?page=8#8