### SI

**(International System of Units)**
(modern metric system)

**SI** indicates the **International System of Units**,
a current, widely-accepted system of the metric units,
standardized internationally and overseen by international organizations.
The system includes refined definitions for a basic set of units
(meter, kilogram, second, kelvin, mole, and candela)
and an extensive set of more specialized units derived from these.
The common metric units (e.g., meter, kilogram) predate the system
and are also used in other similar metric-based systems.

Some non-SI units remain in common use, especially for electromagnetic
measurement, such as for magnetic flux density: in addition to
the SI unit, the tesla, a non-SI (CGS) unit, the gauss,
is still in use. Fields of science and technology sometimes coin
their own non-standard units, at a convenient order-of-magnitude and/or for
a relevant quantity: in astrophysics, among them are the foe,
a unit of energy, and the jansky, a unit of spectral flux density.

(*measurement*)
**Further reading:**

http://en.wikipedia.org/wiki/International_System_of_Units

https://www.nist.gov/pml/weights-and-measures/metric-si/si-units

https://www.engineeringtoolbox.com/si-unit-system-d_30.html

https://www.bipm.org/en/measurement-units/

**Referenced by pages:**

angstrom (Å)

atm

CGS

Gal

gauss (G)

irradiance

Julian date (JD)

joule (J)

jansky (Jy)

kelvin (K)

magnetic flux (Φ)

magnetic flux density (B)

mass

mole (mol)

sidereal

siemens (S)

solid angle (Ω)

Stefan-Boltzmann constant (σ)

tesla (T)

time standard

torr

terrestrial time (TT)

watt (W)

Index