"...each marking is supposed to represent 5/1000's of a degree."
As a surveyor, I was constantly dealing with error; something that is always there in even the most precision instruments available. So, the first thing to do is accept that you'll never get it perfect.
On surveying instruments, bubbles are generally used for rough leveling, and other mechanisms are used to increase the precision. Without knowing the particulars of the level you used, I have my doubts that it can be read accurately at that level of precision. Rotating your bubble level is the sort of method that is used by surveyors in order to eliminate as much error as possible, so you have done what you can within the limits of the tool you're using.
Now, the question remains; if you have a measurement you can trust, is 10/1000's of a degree something to worry about? In the span of a foot, it amounts to a difference of about 2/1000's of an inch; a little less than the thickness of a standard sheet of printer paper.
Agree with Minkwelder. And in my opinion, I would level the platter and not worry about the tonearm. If you want to drive yourself really nuts, you can try to shim the tonearm mount board (don't know what tt you are using, but I assume it's got a mounting board) so as to bring it into line with the platter.
Approximations are just fine in this hobby.
I misread the units of the graduated marking - I now believe each graduation to
represent 5/1000 of an inch.
I had an email from Jeff at Audiomods and he advised that I ensure the platter
Many thanks for the responses - I think I've come to the same conclusion
But - If anyone has a contrary opinion I like to understand the reasoning
Agree with Lewm and Minkwelder and point out that even if the planes of the platter and plinth were perfectly parallel, vinyl records certainly won't be. I have a low percentage of records out of a collection of several thousand that are close to flat.
I should correct something I said earlier. I said "you'll never get it perfect". That's not entirely true. You could very well get it perfect, but there is no way you'll ever know for certain!
The graduations on your level are most likely intended to indicate how out of level the surface is in some fraction of a degree, but don't concern yourself with that. Just use the markings as a reference to verify that the bubble doesn't move as you rotate the level through 360 degrees, and you've done as well as you can realistically do.
If you don't mind, what brand/model of level are you using? I have the Ortofon level. It deviates from dead center to 1/10 of a degree out when spun in place. I think that is 1/20 of a degree error. Not what I expected for $50 but usable none-the-less.
You are being way too anal!
I use a free bubble app on my I phone and it's dead nuts accurate. I've cross checked it with real bubble levels and they zero out after I set it with the iPhone.
agree that with pivoted tonearms 'absolutely perfectly level' is certainly desired at the top of the food chain for ultimate performance, but absolutely dead-on-perfect is not critical for good performance. and really; getting a platter level should be an easily doable thing unless there are other problems. having the drive system aligned properly for best speed is maybe the most critical issue and if the tilt affects that then it ought to be corrected.
personally I have an active isolation base which is self leveling which eliminates the issue for me (assuming my plinth and platter are correctly aligned which with its design it's not an issue as it's one solid construct).
if you have a linear tracking tone arm then it's a whole different ballgame. it's absolutely critical that the arm tube which the arm wand travels along is totally level or undue stress is put on the stylus and cantilever......both from a tracking perspective and a stress failure of the cartridge perspective. with the Rockport Sirius III it was important to check the level of this arm tube regularly and adjust the air suspension to get it level. you would check it by tapping the arm wand (in the up position) to unweight it and make sure it stayed in the same place. if it drifted one direction or the other then you adjusted the air suspension.
so the importance of level varies. I'm not saying it's ever not important, only not to stress too much on the issue when there are bigger aspects to work on.
Syntax - It's all about the journey :-)
Yogiboy - you are correct - But I'm over it now :-)
wlutke - FYI: I purchased two levels from Ebay
Coming from china I figured their quality might be "suspect". Turns out one was actually spot on, but the other was a write-off - guess I got lucky this time
I took everyone's advice and levelled the platter and I actually understand why it's so important - especially with the better cartrdiges.
The arm I'll get to in due course, but for now I'll live with the 1/100" tilt :-)
There are many leveling apps from the Apple app store. Level the platter, then use a Fozgometer to get the cartridge accurately in the groove. I would not shim the arm...you want a solid connection to the turntable arm board.
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.