The second row of numbers is for those times you need to dial more than 5 mils. It's just to make your life easier.

Once you mount it and zero the rifle turn the knob all the way down and record how many turns it took to get there. That way, if you get lost you can return to zero. Or, note what line the turret is on, or get one of the add- on zero stops Skullybones will be making here shortly.