Here's the deal: I use a Sig Saur Kilo 2400 rangefinder. It pairs to your Smartphone app and there are tools in the app you can use to refine your solution, but, and that's a big big but in my opinion, the wind! To make this shot, you need a spotter or spend some time in a spotting scope and look at the wind 1/3 the way, 1/2 the way, 3/4 the way, etc until you can identify a precise wind hold, but, the key is a spotter. The wind changes and changes a lot, and real time changes from a very experienced spotter can make or break you! The Rangefinder gives you the MOA drop and the wind at your position so cold does not make your I phone worthless. The wind is not your friend, and you need to practice in wind to prove to yourself that you have no "*Rule 1 Violation*al" means to assure a lethal shot at 650 yards! That's what I learned playing with the wind in rugged hunting terrain! *Rule 1 Violation*al Solution: get closer! I may get shot down from some highly experienced professionals out there, that's ok, and am all ears to learn, but as a recreational hunter, not competitive marksman or military sniper with a designated spotter on board, my solution is to get closer rather than risk a miss or wound an animal that I cannot ever retrieve!