The Sightron SII Big Sky takes precision shooting to another level with superior quality and innovation. The ExacTrack windage & Elevation turrets out performs the competition in every aspect with positive audible click adjustments. The ExacTrack system maintains a constant point of contact with the erector tube so that there is never mush or drift in your adjustments. The SII Big Sky also features all weather construction with a nitrogen filled tube to eliminate moisture and internal fogging. The precision ground glass is fully multi-coated with ZACT-7 coating for superior light transmission and resolution. The SII Big Sky is in a class of its own and Sightron is so confident you will agree, it is covered by a complete lifetime warranty.