The NIST Reference on Constants, Units and Uncertainty Information at the foundation of modern science and technology from the Physical Measurement Laboratory of NIST

SI Units
Constants,
Units &
Uncertainty
home page
 		 Essentials of the SI
    Introduction
    SI units and prefixes
    Units outside the SI
    Rules and style conventions

Background
    Definitions of the SI base units and their historical context
    International aspects of the SI
    Unit conversions

Bibliography
    Online publications and citations

 

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Online: February 1998  -   Last update: October 2000