Measurement of any physical quantity involves comparison with a certain basic, arbitrarily chosen, internationally accepted reference standard called unit. The result of a measurement of a physical quantity is expressed by a number (or numerical measure) accompanied by a unit.
SI Units
SI Base Units

SI Derived Units:
area  square meter  m^{2} 
volume  cubic meter  m^{3} 
speed, velocity  meter per second  m/s 
acceleration  meter per second squared  m/s^{2} 
wave number  reciprocal meter  m^{1} 
mass density  kilogram per cubic meter  kg/m^{3} 
specific volume  cubic meter per kilogram  m^{3}/kg 
current density  ampere per square meter  A/m^{2} 
magnetic field strength  ampere per meter  A/m 
amountofsubstance concentration  mole per cubic meter  mol/m^{3} 
luminance  candela per square meter  cd/m^{2} 
MKS System
MKS unit of measurement is meterkilogramsecond. SI unit was derived from MKS system. In MKS system length is in meter (m), area is in square meter (m2 ), volume is in cubic meter (m3 ), time in second (s), mass is in kilogram (kg), weight (force) is in kilogrammeter per second square (kgm/s2 ), density is in kilogram per centimeter square (kg/cm2 ), acceleration is in kilogrammeter per second square (kgm/s2 ), force(pressure) is in kilogramforce per square centimeter (kgf/cm2 ).
CGS System
The CGS system was introduced formally by the British Association for the Advancement of Science in 1874. It found almost immediate favor with working scientists, and it was the system most commonly used in scientific work for many years. Meanwhile, the further development of the metric system was based on meter and kilogram standards created and distributed in 1889 by the International Bureau of Weights and Measures (BIPM). During the 20th century, metric units based on the meter and kilogram–the MKS units–were used more and more in commercial transactions, engineering, and other practical areas.
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