Take a ruler and measure the pivot to spindle distance. if it is 222mm, then use one of the Rega arc protractors at vinyl engine. Seb's protractors have served me well. I print it out and tape it on top of an old records...provides solid base and perfect height for cartridge alignment.
not sure what you are trying to do. if you're trying to install the arm, set pivot at 222mm from the spindle (219.5 may be better but we won't get into this).
if you're trying to setup a cartridge, you don't need to know the effective length with either Seb's protractors or, say, the turntable basics protractor (and a couple other ones as well). you do, however, need to verify the pivot to spindle distance is as per Rega spec (222mm).
not sure what you are trying to do. if you're trying to install the arm, set pivot at 222mm from the spindle (219.5 may be better but we won't get into this).
if you're trying to setup a cartridge, you don't need to know the effective length with either Seb's protractors or, say, the turntable basics protractor (and a couple other ones as well). you do, however, need to verify the pivot to spindle distance is as per Rega spec (222mm).