Gemini05,
Expanding on Peter's response, if you're obsessive enough to visually measure SRA, what needs to be measured is the vertical contact line of the stylus. That's what actually interfaces with the modulated grooves of an LP.
As Peter implied, whether this line falls at the front or back face of the stylus or somewhere in between depends on the stylus shape.
FYI, on some styli the contact line is easy to see, on others it's difficult or impossible.
Measuring anything other than the stylus's vertical contact line would produce a number only randomly related to its playback characteristics, not a measurement in any meaningful sense.
P.S. For completeness it should be noted that conical (aka, spherical) styli have no vertical contact lines, just two contact points. The lack of any vertical dimension in their contact surfaces makes SRA mathematically meaningless for conical styli. This explains why SRA changes with such styli are inaudible, which confirms the concept stated in my first paragraph by negative example.
***
So much for theory. As others have stated, visual measurement of SRA is largely a waste of time. The most it can do is put you in the ballpark prior to final adjustment by listening. There are faster, easier and less expensive ways to do that than visual SRA measurement.
You can get in the ballpark in about 30 seconds with no measuring tools, magnification or special lighting. Just eyeball to make the cartridge top surface or (second best) the tonearm visually level to the record surface. That's almost always close enough. Fine tune by listening.
In an unfamiliar system with an unfamiliar tonearm and cartridge, I can optimize SRA for a particular LP in 2-3 minutes. In my own system it's even less, since the roughing in by eye has already been done. USB microscope geeks are still hunting for their tools while I'm listening to music, with SRA optimized at least as well as theirs will ever be. ;-)
Expanding on Peter's response, if you're obsessive enough to visually measure SRA, what needs to be measured is the vertical contact line of the stylus. That's what actually interfaces with the modulated grooves of an LP.
As Peter implied, whether this line falls at the front or back face of the stylus or somewhere in between depends on the stylus shape.
FYI, on some styli the contact line is easy to see, on others it's difficult or impossible.
Measuring anything other than the stylus's vertical contact line would produce a number only randomly related to its playback characteristics, not a measurement in any meaningful sense.
P.S. For completeness it should be noted that conical (aka, spherical) styli have no vertical contact lines, just two contact points. The lack of any vertical dimension in their contact surfaces makes SRA mathematically meaningless for conical styli. This explains why SRA changes with such styli are inaudible, which confirms the concept stated in my first paragraph by negative example.
***
So much for theory. As others have stated, visual measurement of SRA is largely a waste of time. The most it can do is put you in the ballpark prior to final adjustment by listening. There are faster, easier and less expensive ways to do that than visual SRA measurement.
You can get in the ballpark in about 30 seconds with no measuring tools, magnification or special lighting. Just eyeball to make the cartridge top surface or (second best) the tonearm visually level to the record surface. That's almost always close enough. Fine tune by listening.
In an unfamiliar system with an unfamiliar tonearm and cartridge, I can optimize SRA for a particular LP in 2-3 minutes. In my own system it's even less, since the roughing in by eye has already been done. USB microscope geeks are still hunting for their tools while I'm listening to music, with SRA optimized at least as well as theirs will ever be. ;-)