G'day the Forum, Cassian here, I enrolled today, have studied Eric's and Sean's responses, and am inspired. Inspired that a forum is occuring. Full credit to Eric for initiating this site.
The origional draft (PDF) is attached, it was indeed a typo by the AAA, I reckon my origional is not perfectly lined up, the bottom end of the white line is out by a milimitere or so. From my perspective I see the trunk collar in the photograph and regard the union between trunk tissues verses branch tissues as visible (the tree is in my garden), as an arborist my computer graphics skills are lacking.
I whish to make the point that the though I currently work for a Utility company my background is straight Arb, I am the founder and head of the Tree Care division of Eastern Tree Service and that the Tree Culture Course (now 4 years in the making) is an Arborist's interpretation of tree lore as recorded by Shigo and Mattheck. The course is an ongoing development of mine (ours) as I represent a collective knowledge and experience base. As Sean acknowledges I am no expert, merely a student, for me comprehending the parts and processes of trees has no end.
I support Sean's perspective, as a Shigoist I believe we should scrap the concept of arriving at a trunk collar via angles and focus purley on the body of a tree, to arrive at the trunk collar via discernment of trunk and branch tissues.
I also believe that optimal location of a trunk collar has less to do with logic and more to do with tuning in to the tree.
My utter regards to all - Cassian...
Origional version of `Stub Cut' by Cassian....pdf