High quality product from Sniper Tools Design Co. The Sniper Tools Angle Cosine Indicator (ACI,) is a simple tool for hunters in mountainous terrain for determining the angle to the target so that adjustments can be made to achieve the correct Point-of-Impact. The Mil Spec ACI is a vault solid, water proof precision instrument (as per US Military Specs;) quiet, and made from aircraft grade aluminum, which is anodized in a flat black color. The cosine numbers are laser engraved onto the body in 5-degree increments. The lens is shatter proof, shock proof, and resistant to chemicals such as acetone and cleaning solvents. Completely mechanical, there are no batteries or electronics to