what i don't understand is how one can project a perfectly square and lengthwise true shape into a non-perfect piece of wood from one edge. this is what sobon seems to suggest in his book as a way of dealing with hewn timbers. but where do you lay thearm of the square? if that one outside edge you layout from is not perfect, then your 7X7, though it may be a perfect square, may not be aligned along the length of the tree.

the only way to do it exactly seems to be with chalk lines. and even they are a little fuzzy.

the reference has to somehow remain a perfect, symbolic abstraction through the whole process- i.e. map out the ends of the log with vertical and horizontal axes- ideally the center of the tree- use this to square the timber, assume that the timber is neither square nor straight, refer back to the central axis to lay out chalk lines, and use a standardized measure to layout joints from those projected lines.

and then a check opens up 1/16 of a inch and the timber is that much wider.