Yep chicknstripn's description is basically the method I was going to dig up. I just retard the CPS 2 degrees (leave hardware loose) while the mark is just coming up on the left of the window then flip the switch set the mark dead center then slowly slide CPS sensor advance then lock as soon as it primes. The straw thing is good for the first time to compare the mark with the piston, that way you will know for sure. (I may do that actually and scribe the inspection hole to the leading mark edge, not a fan of how wide the margin is on that mark).
Also I wasn't going to have you flash anything, but give you that "visual" cue to do the job.