Parallax on a scope is an inconsistency in the view that you see when you look down the rifle scope. It occurs when the target and reticle are on different planes within the scope. This causes the crosshair to move across the target when the shooter moves their head or eye position, which can lead to inaccurate shots. Parallax can be corrected by adjusting the scopes parallax correction system, which involves a dial on the side of the main tube, often referred to as a “side focus” . This system allows a shooter to adjust the image of the target backward or forward to match the focal plane of the reticle. Another method of parallax compensation is an adjustable objective in which the shooter rotates the objective bell, or part of it, moving the objective lens in and out. Fixed parallax is another form of parallax compensation used by some manufacturers, where the distance that a scope is parallax-free is set at the factory and is non-adjustable. To eliminate parallax, riflescope manufacturers set the parallax at a certain distance or build parallax adjustment into the scope. Riflescopes without a parallax adjustment are generally set to be parallax-free somewhere between 50 and 150 yards. To effectively eliminate parallax, the shooter should move their head behind the riflescope (without bumping the rifle) and look for the reticle to move in relation to the target. If it does not move, the parallax has been eliminated.