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It started more than 200 years ago, with the invention of the metric system.
http://en.wikipedia.org/wiki/SI#History
Answer
In 1948, the General Conference of Weights and Measures (CGPM) charged an international committee, the CIPM*, to 'study the establishment of a complete set of rules for (metric) units of measurement'.
The outcome of this study was a rational system of metric units termed 'SI'.
What else can I help you with?
What is the difference between SI base units and derived units.?
There are 7 base SI units and all other are defined using these 7 base units. See the related question below:[http://wiki.answers.com/Q/What_are_all_the_SI_unitsWhat are all SI units?]
What do you call the principal SI units that are used to derive all other SI units?
The principal SI units used to derive all other SI units are the base SI units. These are the units for physical quantities such as length, time, mass, electric current, temperature, amount of substance, and luminous intensity.
How do derived units differ from base unites?
Seven metric base units make up the foundation of SI. And Specific combinations of SI base units yield derived units. That's why the differ.
What the difference between SI base unit and SI derived unit?
There are 7 base SI units and all other are defined using these 7 base units. See the related question below:[http://wiki.answers.com/Q/What_are_all_the_SI_unitsWhat are all SI units?]
Which units are SI base units?
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What is a SI base unit?
A Joule in SI base units is: 1 kg · m2/s2
SI units are based on multiples of what?
SI is a base 10 standardized system
What unit is in SI base unit?
A Joule in SI base units is: 1 kg · m2/s2
Can temperature be measured with si units?
The SI base unit for temperature is the kelvin.
What is the Si units based of?
Kelvin The SI base unit of temperature is the kelvin.
What are base units when you are measuring length?
The base (SI) unit is meter.
How many SI units?
The SI has 7 base units. These units can be combined in an almost unlimited way to form other (derived) units. The Wikipedia article on "SI derived units" lists some examples.
