Advice on setting VTA


I have set it before, but not exactly certain if I’m going about it the right way. I am generally setting it by eye, eyeballing the botton of cartridge body to get it as parallel as possible, sometimes using a 3x magnifier to assist.  I have also in the past used playing cards as a reference for some cartridges, so I have something to fall back on. Generally using the cards stacked at the tonearm base, similar to using feeler gauges. I’ve read that using an index card on top of record can be a good way to set it due to the parallel lines on the card. My question is what am looking at to get parallel? The bottom of tonearm, top, or the bottom of cartridge? The tone arm is a carbon fiber/aluminum 9 inch pro-ject. It does appear to have a slight taper towards the headshell end of arm.
128x128audioguy85
andirocks-
I've watched Fremer on an Analog Planet video use a USB camera to set SRA , he got it to 93 degrees said it was close enough and would have to fine tune by ear anyways....I don't see the need of the camera then..

Right. That's the thing about cartridges: eyes first, then ears. 

Overhang and zenith (rotation on the vertical axis commonly called "alignment") are set geometrically with whatever method you choose. Everything beyond that is done by ear. VTF is a range, within which you tune by ear. VTA, always by ear. Azimuth, same deal. 

There's no end to the tools some guys will try and push to make up for the lack of listening but really everything can be done equally well if not better by ear. 
This is really crazy making....raise/lower the rear end of the arm. This also increases/decreases vtf, and moves the stylus on the alignment jig....and screws around with azimuth. Every variable makes a difference...it may be a month or so until all the adjustments are as you like them.  Get a couple of pills ready....after 30minutes or so, go to sleep and resume your efforts tomorrow.