From the little bit I think i undrestand, when you torque the nut, in steps, you are constantly taking a resistance reading on the pinion.
By using a inch lb. bar torque wrench, ( not a clicker ) on the pinion nut, when it's turned and in a vise.
If it's a used third member, meaning it just came out of a car before you got it, the torque reading should be 0-1 inch lb.
If it's more, it's too tight and Your bearings may be fried if you used it much
You tighten the nut, you take a reading, over and over till you get to the specified torque.
If the torque isn't reached and your resistance goes up, you remove shims. And start over.
I don't know what specified torque you can get away with.
Use a chevy nut, it won't back off. There's alot of work to this.