Originally Posted by blacksquid
One of the problems is that not all head tube angles are the same.
that has nothing to do with it.
OP you understand how it works correctly.
As far as the standards go with quill stems 80deg, 90deg etc makes sense. With most threadless that doesn't cause they can be flipped. An 80 is usually an 80 or 100. Therefore it makes more sense to quote the angle as +/- 10deg or just 10deg.