There was a long multi-month thread on SMC about tensioning bandsaw blades a "few" years ago (2004?) in which some of the BS guru's like Mark Duginske, Louis Iturra, etc. participated. It dealt with how to do it, what to use, repeatability, and the need for precision, etc., etc. At the time Carter, Iturra, and others had come out with expensive tensioning systems, including Carter's pricey $300 ETG1000 digital tension gauge. One of the guru's, I forget who now (Duginske?), said the markings that come on the Delta 14" and many other similar bandsaws were good enough.
That almost sounded too simple, but somehow logical to me. It got me thinking, so I asked what I thought was a fairly simple question that no one could answer. I asked how blade manufacturers came up with a recommended tension for their blades, which, depending on blade size and metallurgy, can typically range from 15,000 psi to 30,000 psi. Did they use some complex metallurgical/physics/mathematical process? Based on what? No one had an answer, so I offered my speculation which no one could challenge since no one had insider knowledge.
I speculated that blade manufacturers worked backwards- they had one or more of their technicians/woodworkers make a series of test cuts at different tension settings (in different woods and wood thicknesses) and measured the tension setting used for each cut. Then they and/or others judged which cut was the best using some criteria- smoothness, ease of cut, minimal wander, etc. etc. Once they somehow "determined" which cut was the best, the setting that was used became the formal recommended tension. If it was a discrete number 16,125 psi it was probably rounded to the nearest 1000 psi or 5000 psi. As a final check they might test and confirm the setting.
So now, what was really a subjective value took on an objective numerical attribute. As we all know the blade setting can be different for different woods, so frankly now is where experience and practice enters the blade tensioning process. Start with tension marks, simple flutter test, etc. then tweak until the blade cuts the way you want it to. Once you gain experience, setting the blade becomes almost second nature, maybe only requiring a quick test cut or two.