Dual point distributor ID question

Yeah, the dual points have an adjustable vacuum pot. You unscrew the nipple and there is an o-ring and a short stack of washers, or one thick washer. But I have never come across any info about how you actually adjust these. When the original vacuum pot failed, I took it apart to see what the washer pack looked like, to compare it to the NOS one I found on eBay. I made sure it was the same. Now I have 2 spare distributors, one CAP and one not, both with good advance pots. But anyway, the vac advance doesn’t seem to be the issue.