O.K.
I think I've gotten some pretty good answers to my original query.
I just received my book on tank inspection written by THE MAN, Bill High. I understand that visual inspections are not subjective when there are obvious dangerous defects in the tank. However, even Bill admits that there is a gray area between pass and fail which can be wide or narrow depending on the experience and scrutiny of the inspector- "Even with the results of tests and guides for maximum wall loss, the inspector is left with a judgement call. Consideration must be given to where the corrosion lies (objective), how extensive it is (subjective) and how deep it penetrates (subjective, unless the depth can be accurately measured- not estimated)." (Parenthetical notations added by me)
"Judgement and experience must be additional ingredients supplied to the visual inspection process. Both judgement and experience will improve by conducting inspections and from industry-supplied new information."
So, the inspection process is NOT based entirely on science and measurement. There IS some "judgement" and "experience" involved. Whenever any subjectivity is involved in an otherwise objective process, the process as a whole MUST be called subjective. Anything departing from the realm of pure science, whether in part or in whole, is not science at all since speculation has been introduced.
In conclusion, the visual is subjective. Yes, I realize that a line of pitting practically penetrating the wall of a cylinder definitely conststitutes a condemned tank by any standards; But, to say that visuals, as a whole, are objective would be false, and I would be hesitant to sign a release beforehand allowing for the destruction of my tank just based on the "judgement" of one person who may, or may not, have "experience", and who makes a business of selling new and used tanks. I would sure like to see the SCUBA industry authorize a third, neutral, and educated party to perform visuals. But, then again, I do understand that the one's filling the tanks should be the ones performing the inspections.
Thanks for all the great replies.