RE: Pythagorean Theorem?
I can tell you as someone that competes in field archery out to 80 yards, over rough terrain and bizarre angles.......the arc style rangefinders don't get close enough to hit the X ring every time assuming a perfect shot. The best thing you can do is use Ontarget1 or a similar ballistics program and print out a cut sheet showing the correct yardage cut for different distances/angles. I carry one of these with me that is specific for each 3D and Field archery specific setup I use.