Some time back, I posted a description of the horizontal method of measuring wall thickness with a Manson gauge. This is not a recommendation, only a different method. By the way, Mr. Hosford kindly demonstrated the horizontal method to me, yes, on a Manson gauge. Previously, I had been using the vertical method. The drawback of the vertical method is that it is impossible to use at a gun show table. With a helper to hold the barrels in place, the horizontal method can be used on a table.