Since one degree is 1/360 of a turn (or complete rotation), one minute of arc is 1/7004216000000000000♠21600 of a turn (or, in radians, π/7004108000000000000♠10800). A second of arc, arcsecond (arcsec), or arc second is 1/60 of an arcminute, 1/7003360000000000000♠3600 of a degree, 1/7006129600000000000♠1296000 of a turn, and π/7005648000000000000♠648000 (about 1/7005206265000000000♠206265) 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.