English: M16A2 with unmarked aperture rear sight for normal firing situations, zeroing and with the elevation knob for target distances up to 800 meters raised. The flipped down larger aperture, marked 0-2 and featuring a windage setting index mark, is used for moving target engagement and during limited visibility. When the normal use rear sight is zeroed at 300 m with SS109/M855 ammunition, first used in the M16A2, the 0-2 rear sight will be zeroed for 200 m. The apertures on these military sights have an unmarked normal use aperture of approximately 1.8 mm (0.070"), and 0-2 setting with a larger aperture of approximately 5 mm (0.200"), and as such this military sight is not strictly a diopter sight in its normal setting and a ghost ring in its 0-2 setting.