I can't explain it as good as he can, but basically you have to make sure your rotors are true to .003" or you could have problems. And you have to have them turned as an "assembly" (hub and rotor), or you won't get accurate results. Not so much an issue on the Camaro one piece rotors, but difficult on the original Camaro/Corvette two piece "hub and rotor" assemblies.
Ed - do you know of any source for new rotors for a 67-68 two piece setup? I recently rediscovered my original two piece rotor hubs and would like to go back to stock, without having to buy the entire repopped hub/rotor assembly just to get a rotor.