Why use a super accurate cartridge protractor

Precision is mandatory. When we multiply a regular Tonearm by Factor 100, the Arm is about 27.34yd (25m) long, the Cartridge System is about 1.09 yd (1m) high with a Length of the cantilever in the area of 0.55 yd (0.5m) and the contact area from the Diamond is only 0.020 in. (0,5mm) ! Similar is the Mass in comparison. (Another chapter for side wall pressure and diamond polishing...)
A simple example to show what analog reproduction really is ... And why sonic performance can be improved with some care and the right tool.
But honestly, buying new cartridges - and writing about it - create more fun...

I only know that with a Mint and a USB microscope and a Fozgometer/Ultimate Analogue set up record and a lot of patience and chill, I am getting incredible sound out of a Benz Glider SLO mounted on a VPI Classic. If you want to enjoy vinyl to the fullest, you have to really sweat the last 2% of the details to the utmost degree.

Are we not taking it on faith that the great masters of cartridge alignment(!)--Lofgren, Baerwald, Stephenson, etc knew what they were doing even though they disagree amongst themselves? Are audiophiles ready to admit that Rega's (mis)alignment scheme is different from them all yet still sounds fantastic on their current generation of tables? Methinks a paradigm shift is in order here. Geometry is a perfect and exact science, but cartridge alignment is not so perfect. Just as the violin luthier's exact measurements does not produce a Stradavarius, but a skilled craftsman can approach the Strad sound using his experience and creativity. There is still a chasm between art and science-- and music is art.

I am not a mathematician but doesn't the geometry change slightly with every moment when stylus is moving along? So, yes, perfect alignment at every moment would be great if it was possible. The trick is to find an acceptable compomise. By ear.

Dear Cocoabaroque, when Loefgren and Baerwald calculated the respective tangential curves (Baerwald/Loefgren A and Loefgren B), they did do it for monophonic records to be tracked with round styli of approx. 60 µm radius.
Stereo microgroove and fine line or similar styli with polished area of 1µm x 5-6µm weren't in sight at all.
A stereo record's groove is not a homogenous track at all and the differences in radii between the groove's two walls do increase with decreasing distance to the spindle.
In other words: the tracking conditions for a stereo stylus do change ever more towards the groove's lead out.
That's why some designers did choose alignments different from the "old masters" and that's a reason why so many modern audiophile records have rather long dead wax - avoiding the ever more problematic situation close to the inner label.
When Loefgren made his calculation's, our grandfathers were young men and our parents were in pampers. This was almost half a century before micro-ridge, vdH 1 or fine line styli first saw the light of day or the walls of a MFSL LP.
A spherical 60µm needle tracking an old wide groove record has a much easier job.
No worries there about soundstage recreation, increasing differences between left and right groove wall contact areas.
Keep enjoying the discussion - off for 2 week holiday in Africa now,
D.