What about Uni Din?

Dear @mijostyn : I'm not talking of null points, this is what I posted that is one of the input values to make alignment calculations:

"  alignment you are talking about choosed the most inner groove distance around 54mm. ""

R.

Dear @jtimothya @solypsa : First than all to make compartisons between different alignments the first premise to be stricted unchangeable is the tonearm effective length, it’s not the same if we make the comparisons with the same P2S distance because the effective length changes.

In the other side and only as an example:

if we take Löfgren A ( could be B too. ) the difference in tracking distortion between the groove at 69mm and 68mm is : 0.06% .

So, both of you are saying that can be aware of that difference between two concecutive inner grooves?

No one can detect even 0.8% and that tracking distortion is going up or down at each single groove: how can any one be aware when the changes are so small and continuous? and if any one can detect it then something wrong with the alignment or the room/system.

All alignments are a compromise and Löfgren A and B perhaps have the best compromise certainly Stevenson and the mijostyn alignment is talking about  are not the best compromises.

R.

Dear @lewm  : "  They are two different phenomena.. ", agree.

Löfgren A ( example. ) distortion at 139mm is 0.19% and at 75 is 0.42%.

R.

Why doesn't anyone ever mention that the whole idea of alignment by protractor is flawed since it assumes that the Zenith of the diamond is precisely 90.0°?   Zenith being skewed by 0.3° is enough to make alignment A behave as alignment B.  If your diamond Zenith is off by 1.5° it is possible that you will completely miss both null points entirely.  

dave

Its a mess this vinyl thing that we love :)
Sure most carts are a series of imperfect connections, and even with a really good protractor its hard to see everything perfectly. So in comes software. In the end these tools get us in the zone but we use our best tool to finish. Ears.