Having the correct alignment depends on the arm pivot to stylus distance, which is the effective length, the offset angle and the overhang. What Yip is referring to is that the SME V has fixed mounting holes Irather than slots such as you see on many headshells), so the distance from the pivot to the stylus tip is fixed, and to a lesser extent the offset angle (it can be changed slightly by twisting the cartridge in the headshell). For an arc protractor this distance is crucial because it determines the exact arc of the stylus as it moves across the record. Sliding the arm base back and forth will change the overhang but NOT the other two parameters. In order for the MintLP protractor to work correctly he needs to know the effective length as closely as possible. Most cartridges have a mounting hole to stylus tip of about 9.2-9.5 mm but it's best to measure it with a calipers.
4 responses Add your response
If you want a wealth of discussion on this topic (which elaborates on Jim's good response), read the various threads on this forum which cover the MintLP.
Also, know that some cartridge manufacturers publish this offset dimension. The ZYX Universe and Airy-3 come in at 9.0mm.
I have a thread on my forum where I compile these dimensions as I come across a new cartridge. The discussion in this thread gets into some of the details of the geometry as well - essentially expanding on Jim's comments. It's over here: http://www.galibierdesign.com/phpbb/viewtopic.php?f=6&t=75
Thom @ Galibier