Greetings,
From e-mails with Bob (and 10" armboards produced for my Galibier customers), the 10" arm is:
Eff length: 247.000mm, p-s 230.283mm.
If you use 248mm effective length, then the correct BAERWAALD p-s is 231.356mm.
I take it down to 3 decimal places because we CNC machine our armboards. Basically, get it as close as you can, and if you have the SME style mount, you can compensate after the fact ... not so much with the Graham mount.
Download John Ellison's protractor from the enjoy the music site for Baerwaald and Loefgren paramenters.
I have a lot of respect for Bob's engineering, but the alignment gauge has one critical flaw: It doesn't stabilize the unipivot and your results will therefore vary.
It's much better than nothing, but if you own a tonearm of this caliber, then you owe yourself a MintLP or similar quality arc protractor. You want to be able to adjust your overhang/effective length to within .001". It matters.
Cheers,
Thom @ Galibier Design