For bench shooting as stated where you would primarily be shooting for group, it matters not where the group is with regard to the exact aiming point.
Lots of things can alter that and it might vary from session to session. Up/down angles aren't much of an issue unless your shooting in steep mountainous terrain especially when hunting. Best solution is to practice shoot as much as possible so as to get a feel for what happens. By and large a slight hold change on the target will suffice.
But there is no doubt that serious angles at long distances can have a big affect on your hitting what your aiming at, and that can be critical when hunting. There are numerous good methods for determining the information and some have been mentioned. Fact is though some of us cant get enough of modern techknowledgy, and some of us want as little of it as possible.
I have a small device I can put in my shirt pocket if I remember. Its a type of protractor, but designed strictly for angle shooting. When my tripod mounted glasses or the gun is aligned on the target, I can just hold that on and it gives the angle and the percentage difference in yards. It's called a Slope Doper, but frankly we rarely use it.
Virtually all PA l/r hunters use the buddy spotter system, and some also rely on a sighter shot of some type.
Remember this when hunting in steep terrain, the precise information you gathered can be obsolete before you even get a shot off, especially during the rut.