Sights are adjusted for a certain distance. Imagine one is set for 100 yards. If you take a piece of yarn and stretch it straight from the rear sight to the front sight and then forward to 100 yards and another piece of yarn from the barrel to 100 yards, they will cross at that point 100 yards away. If they adjust it to be accurate at 50 yards, that point where they cross would happen at 50yards. The sights are on a slightly downward angle.