There is no precision.

You have to check the the alignment of the frame after bending the rear triangle. You can check alignment with the string test (Sheldon Brown, further down the frame setting page) or a frame gauge. I've done this a bunch of times and usually have to re-adjust the rear triangle a bit after the initial cold set.

Also check the dropout alignment, to make sure they're parallel. Again, Sheldon has a home shop method.

The one tool I think every frame-messer-abouter needs is a hangar alignment tool, which the last and maybe most critical alignment. When the hangar isn't aligned to the wheel, shifting suffers, and sometimes a lot.