A $500 galazan gauge or hosford gauge is not, however.

A real gauge gives real measurements. I would not be interested in owning a gun measured using the Pooch method. The odds of misrepresentation are too high.

Only a real wall gauge is going to measure accurately at the depths necessary to know a gun is safe. A .015" reading at the muzzle of a cylinder bore is irrelevant to safety, a .030" guesstimate 10" from the breech is not trivial.

Get the right tool for the job.