One learns by asking questions and using common sence.
The measurements you need depend on the type of action you are working with but all these can be obtained from the manufactuer or by measuring all areas of a tight action of the same make. Basically if any measurement changes from the pre proof measurement to the post proof measurement then the gun failed!!! Properly hardened steel is up to a point elastic and will spring back to it's origional dementions. if it does not either you are higher in pressure then the action will take or you have a soft action and it will beat it self out of shape over time and become unsafe. If you measurements change during proofing junk it and start over, no gun is worth a life!