Headset top stack heights are all different, so I think it's best to measure height either from the top of the top tube or the top of the head tube. To me it's not numbers but as already mentioned long or short and then it comes down to tuning it up for you personal comfort zone. The engraved hash marks and numbers on some stems are just there so you can keep track of the height above the lock nut if you need to pull it off the bike for some reason and re-install.

Chombi