Take the guesswork out of mountainous distances with this ACI which helps you calculate the distance to your target and is corrected for gravity. This Sniper Tools Design Company mil spec angle cosine indicator is vault solid, waterproof, and made from aircraft grade aluminum with an anodized flat black finish. The numbers are laser engraved in 5 degree increments. The lens is shatter proof and shockproof. No batteries are required. Mil Spec Angle Cosine Indicator ACIMIL-A2