Bill, I'm not sure which type of Manson gage you have, but I believe that only the hanging one is accurate, and it has to have the spring on it to push the barrel away from the rod. The troulble even with this one, if you don't hold the barrel parallel to the rod as you are pushing the barrel farther up, you will get variations in the readings, because now the barrel is acting like a see-saw and the needle will reflect that.

I am only trying to come up with something that can read a barrel's wall thickness in more than a 180 degree arc and still be able to watch the dial needle instead of watching the barrel.

David