Originally Posted by jsharr
the adjustable bevel square does not depend on having the bike level, where the other methods do. Just set it to match the angle between top tube and head tube and then lay it on top of a protractor and you have the angle. I do not own the bubble type angles, I do own the bevel square, but I have never used it for this purpose. heck you could take two pieces of wood that had a straight edge and run a single screw through them and make and angle finder for free with stuff you may have laying around.
aso, it sounds as if this method depends on the top tube being horizontal, which is the case with some road bikes, and most older road bikes (and a few older mountain bikes). but not consistent enough to be one's main method of finding HT or ST angles.
I'd be more confident that my floor is level than I would that the top tube is horizontal when the wheels are level...