The Sniper Tools Design Co. Angle Cosine Indicator - Left Hand Hunter is a simple tool for hunters in mountainous terrain. It is utilized with ballistic targeting software or to obtain the corrected for gravity distance to target. The ACI is a vault solid water resistant precision instrument; quiet and made from aircraft grade aluminum which is anodized in a flat black color. 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 fail and is there when you need it the most!