pinion help

Car sitting on all four wheels? And leveled on the floor?. Take a cheap Harbor or whatever- on the back of the trans, bypassing the seal. Vertical. Get a plus or minus reading. Then turn the rear pinion straight up, at the u-bolt flange.take a reading. Plus(up) or minus.
Then take the trans, which usually down; let's say 2 degrees. Then if the pinion/u-joint flange is down 3 degrees, then you have 5 degrees down.
If the trans is up 2 degrees, and pinion down 3 degrees, then you have (plus 2, minus 3= +1) It is hard to explain.
Tran down 2, pinion down 2= 4 down. etc. I ain't a good explainer.