Another part of dealing with parallax is keeping your head in the same place between shots. I have made a lot of cash betting folks. Here is how the bet goes:
5 tries....only have to be in the exact same place twice. I lay down $500 in cash.
I put one of my rifles in a large vise, tightened down where it cant move. Set up two dial indicators on magnetic bases. Get the shooter on the rifle. Take a Sharpie, mark two places on the side of their head. Move the indicators to those marks and zero. Shooter gets off the rifle, then back on 5 times. I give as much time between as wanted. Shooter then looks at the entire video to see he was not scammed. Then pays me $500. I haven't lost this bet yet. I haven't had a shooter yet that can get back on both marks, let alone to zero.
We aren't nearly as good at this as we think.
Charlie

P.S...the bet is good for anyone with some extra cash. Or some gun stuff.

The data and opinions contained in these posts are the results of experiences with my equipment. NO CONCLUSIONS SHOULD BE DRAWN FROM ANY DATA PRESENTED, DO NOT, UNDER ANY CIRCUMSTANCES, ATTEMPT TO REPLICATE THESE RESULTSj