Tonearm adjustments on the fly

We need to understand that accurate reproduction of wiggles in a microscopic groove can only be achieved if there is a fixed spatial relationship between the TT main bearing and the stylus tip. Otherwise the stylus transmits movement that is not driven by the passing modulated groove.

This fixed relationship must be obtained whilst allowing the arm to move in two planes, so the bearings that do that must have no movement other than those, i.e. no chatter.

This is difficult enough to achieve without building into the spatial relationship three or four more adjustments on the fly.  These will necessarily allow unwanted movement that will break the fixed relationship between stylus tip and main bearing.  Remember we are talking about movements of less than 1000th of 1mm.

In any case it is not necessary to adjust azimuth once it is correctly set.  However thick, all LPs are flat (unless they are warped - and should be discarded).

Accepted VTA on the fly is useful to correct the small differences in thickness between discs, but this is the easiest geometry adjustment to achieve without unwanted movement, by raising the arm pillar using a rack and pinion with low geared adjustment via a wheel control that can be calibrated to achieve total accuracy for a record of known thickness when correctly set up at a base value.

Leave the rest well alone.

Unless you can make adjustments from your listening position Vernier adjustments are not a good thing. A tonearm has to be fixed rigidly to the same structure as the platter. This helps drain vibrational energy away from the arm. It also assures the proper orientation of the stylus to the groove as long as you still have the eyesight to set it. Those nasty grub screws have a purpose. Spurious structures also tend to resonate. The most important asset are appropriate scales so you can return to your settings instantly. For most of us tonearms are set it and forget it devices. The more you fiddle with your arm the more likely you are to break something by mistake. I know somebody whose shirt sleeve just got caught under the arm reaching for an adjustment. He ripped the cantilever off. Those of us with workshops know you never work on anything with long sleeve shirts on. Usually it is just you that get hurt. Let's see, what's worse, getting sucked into your 15" jointer or ripping off your cantilever?

Right on Clearthinker, except I doubt anyone can hear the difference between record thicknesses. The actual VTA used to cut records is not constant but can vary a few degrees. I think this is just an example of audiophile nervosa.

A nice test. Turn the volume down and put your ear down by the record. Ladies make sure your hair is tied back, same for guys with long hair.
Listen to your arm tracking the record. Ideally you should here nothing. What you do hear is vibrational energy that is leaving the system and reflecting back on the stylus. If you can hear it so can't the stylus! The quieter it is the better your set up. 

Yes, too much time and electrons have been wasted on trying to make the SRA/VTA differentiation understandable or pertinent.

I've heard/read Michael Fremer and Harry Weisfeld mention that any cartridge - even an expensive one - with a glued-on stylus is more likely than not to be askew in some form (tilted, rotated), so that for me throws any talk of getting the cartridge/tonearm/cantilever parallel with the record out of the window as a definitive suggestion.  It's a good starting point and if you want to obsess with the measurements you certainly can, but ultimately you have to like the way it sounds.  I can't talk for anyone else, but I've never had a come-to-Jesus moment after making the suggested adjustments - usually minor tweaks - using various test records or multimeters (haven't sprung for a digital oscilloscope quite yet), and have always adjusted it to sound good to me; if I can't hear a difference, I set it at the recommended setting and go on with my life.

Thanks Millercarbon for reminding me of the words pedantic, polemics and noobs.   

Erudition elevated. Check. Thanks!