belt drive primary

I replaced the belt on my bike yesterday. I came across a way to set up the alignment. I used two carpenters squares, one 6"x12" for the engine pulley and a big one for the clutch basket. Small side of the engine pulley' square against the pulley, long side on the basket's up against it. Let the perpendiculars meet in the middle. Tells you if they're parallel to a gnat's ass.