The following section in Diopter Sight is incorrect in one of the notes:
Civilian AR-15 target sights have an aperture between 1 and 1.15 mm (0.039 and 0.045 in). The aperture on AR-15 military sights have a day aperture of approximately 1.78 mm (0.070 in), and the M16A2 also a night setting with a larger 5.08 mm (0.200 in), and as such the military sight is not strictly a diopter sight in either setting.
The different apertures on AR style rifles (including the M16A2 referenced) are not "day" and "night", they are for different ranges. Generally speaking it is 0-200m and up to 500m, although some sights use apertures designed for different ranges.
