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# Special Publication 811

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A. Thompson and B. N. Taylor

NOTE:  The BIPM SI Brochure (9th Edition) was published on May 20, 2019. The NIST SP 330 2019 version has been published and reflects the changes incorporated in the BIPM SI Brochure (9th Edition). This publication, Special Publication 811, has not yet been updated to reflect the changes in the SI that came into effect on May 20, 2019 (World Metrology Day).

SP 811 is also available as a PDF file. Some browsers may not display this document as author intended. If in doubt, please use the pdf version.

A related publication is SP 1247 the SI Base Units Relationships Poster (PDF). This publication is a colorful poster illustrating the relationships of the International System of Units (SI) derived units with special names and symbols and the seven traditional base units. The diagram is aligned with the BIPM SI Brochure, 9th edition and NIST SP 330, The International System of Units (SI), 2019 edition. The previous edition of this diagram was published on the back cover of NIST SP 811, Guide for the Use of the International System of Units (SI), 2008 edition.

The traditional SI base unit symbols are shown within rectangle shapes, with the unit name shown above the corresponding rectangle. The derived units with special names are shown in circle shapes, with the unit symbol and name within the circle. An expression for the derived unit in terms of other units shown in parenthesis. Derived units without special names are not illustrated. In the diagram, the derivation of each derived unit is indicated by arrows that bring in units in the numerator (solid lines) and units in the denominator (broken lines), as appropriate. The unit "degree Celsius,'' which is equal in magnitude to the unit "kelvin," is used to express Celsius temperature t, defined by the quantity equation t = T - T0, where T0 = 273.15 K, the ice point. This equality is indicated in the diagram by the symbol K in the °C circle. The numerical value of a Celsius temperature t expressed in degrees Celsius is given by the equation below "CELSIUS TEMPERATURE.'' A difference or interval of temperature may be expressed in kelvins or in degrees Celsius.

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