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- ISO 31-1

**ISO 31-1** is the part of international standard ISO 31 that defines names and symbols for quantities and units related to *space and time*. It was superseded in 2006 by ISO 80000-3.

Its definitions include:

Quantity | Unit | Remarks | |||
---|---|---|---|---|---|

Name | Symbol | Name | Symbol | Definition | |

angle, (plane angle) | α, β, γ, ϑ, φ | radian | rad | 1 rad = 1 = 1 | |

degree | ° | 1° = rad | There is no space between the number and these superscript-style unit symbols. Decimal subdivision of degrees is preferable (i.e., 12.5° instead of 12°30′) | ||

minute | ′ | 1′ = ° | |||

second | ″ | 1″ = ′ | |||

solid angle | Ω | steradian | sr | 1 sr = 1 = 1 | |

length | l, L | metre | m | The metre is the length of the path travelled by light in vacuum during a time interval of of a second; see speed of light | |

breadth | b | ||||

height | h | ||||

thickness | d, δ | ||||

radius | r, R | ||||

diameter | d, D | ||||

length of path, (linear) displacement vector | s, s | ||||

distance | d, r | ||||

cartesian coordinates | x, y, z | ||||

radius of curvature | ϱ | ||||

curvature | ϰ | reciprocal metre | m^{−1} | ϰ= | |

area | A | square metre | m² | The units are (1 a = 100 m²) and hectare (1 ha = 100 a) are used for agrarian areas. | |

volume | V | cubic metre | m³ | ||

litre | L, l | 1 L = 1 dm³ | The capital L is preferred as the small l can be indistinguishable from the number 1 in some fonts. | ||

time, time interval, duration | t | second | s | The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom | Representations of time of day are defined in ISO 8601. |

minute | min | 1 min = 60 s | |||

hour | h | 1 h = 60 min = 3 600 s | |||

day | d | 1 d = 24 h = 1 440 min = 86 400 s | |||

angular velocity | ω | radian per second | ω= | ||

angular acceleration | α | radian per second squared | α= | ||

velocity | v (general symbol), (velocity vector),vc (propagation speed of waves),u, v, w (components of a velocity c) | metre per second | |||

kilometre per hour | |||||

acceleration, acceleration vector | a, a | metre per second squared | 1 g = 9.80665 | ||

acceleration of free fall, acceleration due to gravity | g |

Annex A of ISO 31-1 lists units of space and time based on the foot, pound, and second.

Annex B lists some other non-SI units of space and time, namely the gon, light year, astronomical unit, parsec, tropical year, and gal.