Lukher 3-9x40 Tactical Rifle Scope Red & Green illuminated Mil Dot 20mm Picatinny on weaver or picatinny rails Look through scope within 3 or 4 inch distance from your eyepiece lens. If you cant's see the reticle clearly, loosen knurled lock ring and rotate eye bell until the reticle appears clearest. Then screw the lock ring the eye bell firmly. Rotate scope tube so that vertical crosshair is vertical and horizontal crosshair is horizontal.Adjust the position of scope on the rifle so that proper eye relief is achieved. Then tighter all screws to fix scope on the rifle firmly. Keep scope in the place free from acid, alkaline and other corrosives. Dust and dirt on the surface of scope should be cleaned with soft cloth or soft tissue with a little alcohol.