Thoughts on VTA......

For me, having a C Through design ruler helps with making quick approximate references. If I notice that my tonearm is level, then I've found that I prefer it raised slightly at the head-shell for a fuller sonic signature. This may cost me a little in retrieving detail but after all, it's vinyl, so I don't expect a lot of detail. I do need a better tonearm however.

how can you use different platter mats ......every one sounds different.  I find rear arm height makes little difference when near the "ideal" whatever that is.....however correct azimuth is a huge deal for quality sound.

Azimuth is a huge deal but with a mono cartridge, vertical tracking is inaudible, even with a true mono cartridge.

I do it by ear:

When I setup a new cartridge, whatever album I put on first, I also play via Tidal at the same time (or as close as I can) then I sit back and switch inputs and listen to both.  

I keep adjusting my tonearm until the vinyl sounds as good/better than the Tidal stream.

When my VTA/Azimuth/VTF are off, it's quite clear that the Tidal stream sounds better.

Once I'm happy with the arm setup, I leave it there permanently, until I switch out for a new cart.  Then repeat.

This is why Rega does not allow VTA adjustments even on their best arms. What you lose in rigidity for On The Fly adjustment against what you gain is not worth it. Not to mention the wasted time that you could be listening to the music. Set your VTA on your most favorite record by whatever method that you can and leave it alone. But do check it every 6 months by that method and adjust if needed, parameters do change overtime for various reasons. 

None of the above approaches mentioned in this thread are wrong or invalid since this is about pure physics.

But then again I am getting old and want to enjoy my time listening to music not performing physics experiments :-)