I don't think you read with understanding to well. You sight in your rifle before you hunt. You don't sit and try to account for spin drift and which direction you are shooting before you shoot at your game....well at least I don't.
I sure do
Let me put it another way. How many times have you ever heard "Oh hell I blew the shot of a lifetime because I set my scope to shoot West and the deer was to the East. Forgot to reset my scope to account for spin drift variance. "
Or... "Oh hell, I blew the shot of a life time because I didn't have the right dope"
You will never know how much it has cost my generation to preserve your freedom. I hope you make good use of it.
~ John Quincy Adams