I'll open this subject up here as well. Adjusting my drive belt and manual says 11/16-3/4 in,my bikes jacked up,wheel raised. Where on a "ROCKER" do they measure to get that reading? The bloke at the bike shop yrs ago,grabbed the belt at the bottom,(Where the tension gauge is used,which I have) and said "if you cant twist the belt 90deg,its good" I thought that was a bit how ya goin!! I understand the tool and how it works,but exactly do I put a ruler. A "point A to point B" exact area is what I need. I can ring a shop,any fucking shop,tomorrow,but now would be cool....
midway between front and rear pulley, like as in figure 1 on the illistration you posted.
not sure about yours, but some bikes have a little window in the lower belt guard that has gradient lines on it
Any standard belt deflection is done at mid point between pullies.