Platter Levelling Issue


I have just purchased a new "bullseye style" bubble level that has graduated markings on it to allow you to determine the degree of misaligned conditions - each marking is supposed to represent 5/1000's of a degree

I initially verified it's accuracy by levelling a flat surface and then rotated the level in the horizontal plane in place - the position of the bubble did not move as I rotated it through 360 degrees.

I then placed the level on the plinth by the base of the arm and levelled the turntable - I believe the mounting method of my arm should ensure the arm is now perpendicular.

I then place the level on my turntable platter and took a readings as I rotated the platter through 360 degrees

Turns out the platter is not quite parallel to the plinth
- I don't think the bearing is damaged, since the degree of misalignment was consistent and always in the same direction as I rotated the platter - so the platter is not quite aligned with the plinth

The margin of error I observed is 10/1000's of a degree according to the gradations on the level

So, until I can rectify this - my questions are...

1. should I ensure the platter is level at the expense of a perpendicular arm

2. should I ensure the arm is perpendicular at the expense of a horizontal platter alignment?

3. Am I being 10-1000's of a degree anal :-)

The arm is an Audiomods Series 3 that has Rega style bearings and from what I have read on the web it is more important for arms with a bearing system like the Rega to be perpendicular

I have read other posts on Agon of a similar nature, but there was no mention as to the degree of misalignment

Any input would be very much appreciated

Many Thanks
williewonka
Stringreen's approach (leveling platter and then making sure azimuth is correct) makes sense to me to the extent that I understand the geometry and forces involved. However I would be quite hesitant to use an iphone app. As Doug Deacon has pointed out, the accuracy of that app would depend on a properly square,plumb, and level iphone case, at least with respect to the circuit board inside. I would be willing to bet some real $$ that Apple does not have a spec for that in their requirements for their manufacturers, and if they do, I cannot imagine that the tolerances are anywhere near what people have been talking about here. This is just a theoretical concern, not in any way suggesting that Stringreen or anyone else's set-up is in any way "wrong" or not optimal. In fact, I am pretty sure it's better than mine!
The concern for the app isn't really warranted. You set the Iphone flat, hit "calibrate" rotate 180 degrees and hit "calibrate" again. It's this roation that zeros out the level so its acurate. Again, I cross checked it with very precise "real" level and it was dead on.
I use the Cartridge Man digital level. I know when perfect level has been achieved, and it does make a noticeable improvement in tracking and performance. Yes, it's expensive, but IMO, worth it for a unipivot tonearm (3D arm on my SSM rimdrive).
Thanks for that info, Last. Still not sure I'd trust an iPhone app IF I thought that this was a measurement that had to be accurate to within thousands of an inch, but it's good to know that the issue of the case is taken out of the equation.