Visual setting, even with a microscope, is only getting you into the ballpark. Its plenty good enough and if your arm makes VTA setting a chore then eye ball it, relax and enjoy.
If however your arm is designed for fine tuning, and especially if it allows VTA on the fly, then you can do a whole lot better. Yes SRA is what you really are adjusting. The stylus however sits on the end of the cantilever. When playing a record the whole thing swings up and down and all over the place. The stylus never just sits there static like it will be if you take a picture. So its a waste of time. What you care about is where it is while playing music. For this you have to be playing music. Which makes microscopes impossible. But you can always hear the effect of better SRA. So here's how you do it:
Warm everything up, put on any record you like. Listen. Lower VTA. Lower the back of the arm down a bit. When I say a bit- 1mm is a lot. Even .1mm is a lot. We're talking fine tuning here. So fine tune.
Lower it a bit and listen. The sound will be fuller, warmer. The initial attack of notes will be a bit less sharp and aggressive. You will know right away if you went the wrong way or the right way. If you're not sure no problem, simply either raise it back up or lower it even further down. Once you do this even a few times you will get the hang of it and you will know.
Then it becomes a process of very small changes. Let's say it sounds better when you raise it. So keep raising it, listening, raising, listening, a very tiny amount each time. Eventually one time when you raise it instead of it becoming more detailed and clear it will become thin and instead of the bass getting tighter and more defined it will just seem a bit less. You went too far. So back it off a bit. Lower it back down.
At this point you find out just how picky you are. Already the sound is far better than eyeball. By a process of interpolation you can get to where its dead on. But only for that one record! Next one may sound better a little higher or lower. We're talking tiny differences.
This is where most will call it good. Which believe me if you did this it is plenty good! The next step will be to do this with several of your favorite records. After a while you will notice there's one setting that is just about perfect for the vast majority. You're done.
Unless... its possible on some arms to write down the VTA setting on the record sleeve so that next time you can play it with perfect VTA. Not just really really close, perfect.
There's no right or wrong. No matter what you might think the stylus isn't sublimely gliding its bouncing around the groove all the time anyway, so being off a bit isn't doing any harm. Its all down to how much you enjoy the results of perfect vs how much you enjoy the fuss of getting it there.
