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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.
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′) |
| arcminute |
′ |
1′ = (1/60)° |
| arcsecond |
″ |
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 |
s |
| distance |
d, r |
| cartesian coordinates |
x, y, z |
| radius of curvature |
ϱ |
| curvature |
ϰ |
reciprocal metre |
m−1 |
|
ϰ=1/ϱ |
| 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 |
|
| 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 = 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),
c (propagation speed of waves),
u, v, w (vector components of a velocity c) |
metre per second |
m/s |
|
|
| acceleration |
a |
metre per second squared |
m/s² |
|
|
| 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.
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