The cap surface is not the centerline of the bearing. I'm not the smartest apple in the bunch but have checked that before and it is not accurate. Not trying to be a smartass either so please take my opinion for what it is worth. I have set up a few hundred rear gear sets in my life time thou... If you get the pinion depth correct on a good set of gears it comes out perfect 99% of the time. Everyone does it a little different and whatever works for you is good. I have the tools due to doing it at work often. It is difficult to spend the money if only doing it a couple times in a life time.