Very interesting topic. I recently bought the $100 Manson gauge from Brownells and found that it can be difficult to get an accurate reading. Worked best for me vertically when tied to a string hanging from a rafter. Directions say not to use horizontally and that's true as there is 0.020-0.030" flex just from the weight of the tool. I'm not sure how I'd use at a gun show without bringing a ladder to hang it from the ceiling, so much for the portable benefit.

I'm interested to learn more about how to get accurate & reliable wall thickness readings. Thanks.