AO indexing is just to get it close, none of mine are exact even on my elite 4200. Simple way is to place the rifle on bags so it is stabile, adjust the AO to a target at 100yds, or 50yds, whatever. Look thru the scope and move your head around while watching the reticle on the target. When the AO is correctly focused, the reticle will not move on the target. If the reticle moves when you move, the amount of movement on the target is the parallax error. If shooting at a known range, I make a mental note of the AO position for future reference. Some shooters make new marks, it's up to you. Hope this is clear, no pun intended. :wink:
Tim