tim,
good point about offsetting the tenon to keep the holes accurate if you are drawboring by the numbers.
we've been scribing mostly for a while so our tenons are pricked when the bent/wall/truss is assembled and then pulled apart and the tenons drilled.
if we're square ruling, if the surface is pretty good, we use either a drill guide or on irregular stuff, we level the stick use a level to guide the bit.
