Minute and second of arc
（重定向自Arcmin）
A minute of arc, arcminute (arcmin), arc minute, or minute arc is a unit of angular measurement equal to one-sixtieth (1/60) of one degree. As one degree is 1/360 of a circle, one minute of arc is 1/21600 of a circle (or, in radians, π/10800). A second of arc, arcsecond (arcsec), or arc second is 1/60 of an arcminute, 1/3,600 of a degree, 1/1,296,000 of a circle, and π/648,000 (about 1/206,265) of a radian. These units originated in Babylonian astronomy as sexagesimal subdivisions of the degree; they are used in fields that involve very small angles, such as astronomy, optometry, ophthalmology, optics, navigation, land surveying and marksmanship.