Yall are barking up the wrong tree. You don't use a caliper to setup a rear end, but I *have* seen it done with a dial indicator and a magnetic base. The amount indicated on the dial (total) divided by 2 = the clearance when you rock the gears back-n-forth just enough to make contact.
Watched my boss setup a few Rockwell rears that way. It still took him a few days for each one (they were new parts and super-expensive) so he was real careful to do it right the first time.
I decided to just pay somebody else to do mine when I get the chance to re-gear.
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