Scopes intended for long ranges will typically have multiple markers for multiple ranges. I.e., along one long vertical line, you have a specific horizontal line for 100 yards, and another one for 200 yards, and another one for 300 yards, etc.

These account for basic bullet drop, but then you will have to do some on-the-fly adjustment for things like wind. This is one of the reasons why, in the military, someone in a "sniper" role often has a "spotter"... the recoil action of the rifle might throw the sniper's viewing window way off and require him to have to re-aim all over again the for next shot, but the spotter has an unaffected view of where the last shot landed to help the sniper recalculate the next shot.