ISO 31-1

In this article we are going to delve into the exciting world of ISO 31-1. Throughout history, ISO 31-1 has aroused great interest in humanity, whether due to its impact on society, its relevance in the scientific field, or simply because of its influence on popular culture. From its origins to the present, ISO 31-1 has played a fundamental role in people's lives, becoming a fascinating subject of study for experts and hobbyists alike. Through this writing, we propose to explore the different facets of ISO 31-1, analyzing its importance and its impact in various areas.

Part of international standard ISO 31

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ISO 31-1^[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 It was superseded in 2006 by ISO 80000-3.

Definitions

Its definitions include:

Quantity		Unit			Remarks
Name	Symbol	Name	Symbol	Definition
angle, (plane angle)	α, β, γ, θ, φ	radian	rad	1 rad = 1 m⁄m = 1
		degree	°	1° = π⁄180 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′ = (1⁄60)°
		second	″	1″ = (1⁄60)′
solid angle	Ω	steradian	sr	1 sr = 1 m2⁄m2 = 1
length	l, L	metre	m	The metre is the length of the path travelled by light in vacuum during a time interval of 1⁄299 792 458 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
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	rad⁄s		ω=dφ⁄dt
angular acceleration	α	radian per second squared	rad⁄s2		α=dω⁄dt
velocity	v (general symbol), v (velocity vector), c (propagation speed of waves), u, v, w (components of a velocity c)	metre per second	m⁄s
		kilometre per hour	km⁄h
acceleration, acceleration vector	a, a	metre per second squared	m⁄s2	1 g = 9.80665 m⁄s2
acceleration of free fall, acceleration due to gravity	g

Annex A

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

Annex B

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

References

1. ^ "ISO 31-1:1992". ISO. Retrieved 2023-02-07.

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