Detachable sights are a great option to back-up or cowitness with optics. This GG&G sight is spring-actuated and has a locking detent. The detent release is located on the left hand side so the offhand has quick and easy access to let the sight down. The Multiple Aperture Device (MAD) designation refers to the sight having four apertures, two of each sizes 0.073" and 0.199". Each click changes the aperture viewed.