Steve,
When I was into vinyl (Monaco TT, Triplanar VII & various cartridges but favourite was Len "The Cartridgeman" Gregory modded Music Maker Sapphire with a Glenn Croft MM phono) I initially got hung up about SRA, and learnt how to set up a cart on my system with a USB microscope. Then I read that for an arm with a 300mm effective length, to get a one degree change of SRA you need to alter arm height by 5.23mm. A 1.0mm change in arm height changes SRA by 0.19 degrees.
After that, a gave up on the scope method, and when setting up a cart, eye balled it to roughly parallel to the record surface, and depending on the cartridge, and the pressing (the cutting angles of disks can vary, I understand, by up to 20 degrees) lower or raised VTA to hit the sweet spot if something obviously needed it. Or I wanted to fine tune the sound for my system - tail down, tail up etc. Or just wanted to have a play with my kit.
The modded Grado's that Len makes are a nightmare to set up - they are super fussy with VTA - borne of a very long line contact stylus with the record - but on the plus side it is easy to hear when you have them correctly dialled in - the sound would suddenly lock into place. Great carts btw - sort of a cross between MC and MM, but without the issues of either (they have their own issues - mainly set up and compliance).
If you are interested, Geoff husband wrote an excellent piece on TNT about VTA/SRA here:
http://www.tnt-audio.com/sorgenti/vta_e.html. I like Geoff's writing - no nonsense approach to hi fi.
That said, I had much fun with the Triplanar, raising and lowering the VTA on the fly, if for no other reason than I liked to fiddle and could convince myself I had made a positive change to my listening experience after each such intervention. Mind you, a clean record makes much more of a change. And VTF even more.
Vinyl is so much fun, and if I had the budget, the time and the space, and could overcome my OCD with it, I'd be pretty keen on a decent vinyl rig again. Nothing sounds like vinyl done well. Fortunately, I have some really good friends I can annoy on a regular basis for my vinyl fix.
Speaking of which its about time for another top up of vinyl goodness...