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A second of arc, arcsecond (arcsec), arc second, or second arc is a unit of angular measurement equal to 1/3600 of one degree.
A angular mil is the unit of angular measurement equal to 1/6400 of a complete circle. At 1000 metres one mil subtends about one metre (~0,98 m). Also 1/6000 and 1/6300 are used in other countries.