Your holdover points will always be the same relative ANGULAR elevation over your set zero -- the thing is, the bullet obviously starts dropping more as your shots get farther out.
Basically you'll want to found out what your elevation points are in MOA (or MILs) over your center cross hair. If you can't find the data in documentation, you could figure this out with a properly marked target set up at 100 yards (1 MOA = 1.047" at 100 yards). You can just look at your reticle and see what hash marks it lines up with to figure out how many MOA of elevation each mark gives you
Then you'll need to use some ballistics software (there are some free online ones) to figure out your drop chart in MOA, relative to your zero. For example, your drop chart for a .300 RUM might look like this (Distance in Yards : MOA of drop):
300 : 0
400 : 2.0
500 : 4.25
600 : 6.5
700 : 9.25
800 : 12.25
900 : 15.5
1000 : 19.25
So if that's your drop chart, and you figure out that your reticle elevation marks art 4, 8, and 12 MOA -- then the ticks would correspond to a bit under 500 yards, somewhere between 600-700 yards, and just under 800 yards. Of course, if you do your drop chart in increments of 5 yards or something, you can get much more precise drop values for your scope markings.
Anyway, I think the important concept is that the hash marks will always give you the same angular elevation over your zero -- so just think in terms of MOA of elevation over your zero.
Hope that helps.