You can see the parallax error by looking thru the scope while the rifle is in a solid rest while changing your eye position, aim at a target at the range you want to check it at, look thru the scope without moving the rifle, move your eye position slightly and you'll see the X-hair move in relationship to the target, you'll get an idea how much your eye position can affect POI. When shooting at targets placed at the same range as the scope is parallax error free(50yds in this case), the X-hair won't move when you change eye position.
Tim