Sonic checkers

Good idea,,so you did this with the stock probe,,if so we maybe lucky as that even smaller i.d than a 4" cylinder,,which means a smaller radius.. now i wonder how the ruff rust scale that can be on the back side of a cylinder wall will effect the test,,some of it can be pretty dence and that might cause any tester to fluctuate,,of course practise will show how to deal with it,,wayne