The International System of Units (abbreviated "SI") is a scientific method of expressing the magnitudes of seven important natural phenomena. This system was formerly called the meter-kilogram-second (MKS) system. All SI units can be expressed as a standard multiple, fractional quantity, and also directly. Multiple and fractional SI units are defined by prefix multipliers in powers of 10 ranging from 10^{-24} to 10^{24}.

International System of Units

**Ampere:**(abbreviation, A)

Ampere is the SI unit of electric current. One ampere is the current that would produce a force of 0.0000002 (2 x 10^{-7}) Newton between two straight, parallel, perfectly conducting wires having infinite length and zero diameter, separated by one meter in a vacuum. One ampere represents 6.24 x 10^{18} unit electric charge carriers, such as electrons, passing a specified fixed point in one second.

**Candela:**(abbreviation, cd)

Candela is the SI unit of luminous intensity. It is the electromagnetic radiation, in a specified direction, that has an intensity of 1/683 (1.46 x 10^{-3}) watt per steradian at a frequency of 540 terahertz (5.40 x 10^{14} hertz). Note: A steradian is a unit of measure equal to the solid angle subtended at the center of a sphere by an area on the surface of the sphere that is equal to the radius squared.

**Kelvin:**(abbreviation K), also called the degree Kelvin (abbreviation,

^{o}K)

Kelvin is the SI unit of temperature. One Kelvin is 1/273.16 (3.6609 x 10^{-3}) of the thermodynamic temperature of the triple point of pure water (H_{2}O).

**Kilogram:** (abbreviation, kg)

Kilogram is the SI unit of mass. It is defined as the mass of a particular international prototype made of platinum-iridium and kept at the International Bureau of Weights and Measures. It was originally defined as the mass of one liter (10^{-3} cubic meter) of pure water.

**Meter:**(abbreviation, m)

Meter is the SI unit of displacement or length. One meter is the distance traveled by a ray of electromagnetic (EM) energy through a vacuum in 1/299,792,458 (3.33564095 x 10^{-9}) second. The meter was originally defined as one ten-millionth (0.0000001 or 10^{-7}) of the distance, as measured over the earth's surface in a great circle passing through Paris, France, from the geographic north pole to the equator.

**Mole:**(abbreviation, mol)

Mole is the SI unit of material quantity. One mole is the number of atoms in 0.012 kilogram of the most common isotope of elemental carbon (C-12). This is approximately 6.022169 x 10^{23}, and is also called the Avogadro constant.

**Second:**(abbreviation, s or sec)

Second is the SI unit of time. One second is the time that elapses during 9.192631770 x 10^{9} cycles of the radiation produced by the transition between two levels of Cesium 133. It is also the time required for an EM field to propagate 299,792,458 (2.99792458 x 10^{8}) meters through a vacuum.