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Systems of Units and Notations
Systems of Units
A measurement of any
physical quantity must be expressed as a
number followed by a unit.
A unit is a standard by which a dimension
can be expressed numerically. The units
for the fundamental dimensions are called
the fundamental or base units.
While carrying out calculations,
there are several systems of base units
that are available. However, the most common
one is the International System
of Units (also called SI,
from the French "Système International
des Unités") introduced by Griorgi
in 1901, including the meterkilogramsecondampere
(MKSA) subsystem representing the
four fundamental dimensions length,
mass, time,
and electric current, respectively.
The units for other dimensions are called
secondary, or derived
units and are based on the above fundamental
units.
This portal employs the
SI units that are commonly adhered to by
virtually allengineering professional societies.
 The SI is the standard system used
in today’s scientific literature.
 The SI has seven base units, several
derived units with special names, and
many derived units with compound names.
 In addition to the units, the SI system
involves other recommendations, one
of which is that multiple and submultiples
of the MKSA units be set in steps of
10^{3} or 10^{3}.
The fundamental SI units
and abbreviations are listed in Table 1.
Table 1 The Seven
Fundamental SI Units
