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 Decisions relating to the base units of the SI
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Length:
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1st CGPM, 1889 |
sanction of the prototype metre |
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7th CGPM, 1927 |
definition and use of the prototype metre |
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11th CGPM, 1960 |
redefinition of the metre in terms of krypton 86 radiation |
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15th CGPM, 1975 |
recommends value for the speed of light |
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17th CGPM, 1983 |
redefinition of the metre using the speed of light,
realization of the definition of the metre |
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CIPM, 2002 |
specifies the rules for the practical realization of the definition of the metre |
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CIPM, 2003 |
revision of the list of recommended radiations |
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CIPM, 2005 |
revision of the list of recommended radiations |
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CIPM, 2007 |
revision of the list of recommended radiations |
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23rd CGPM, 2007 |
revision of the mise en pratique of the definition of the metre and development of new optical frequency standards |
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CIPM, 2009 |
updates to the list of standard frequencies |
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24th CGPM, 2011 |
on the possible future revision of the International System of Units, the SI |
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24th CGPM, 2011 |
revision of the mise en pratique of the definition of the metre and development of new optical frequency standards |
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CIPM, 2013 |
updates to the list of standard frequencies |
We are pleased to present the updated (2014) 8th edition of the SI Brochure, which defines and presents the Système International d'Unités, the SI (known in English as the International System of Units).
- SI prefixes
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Factor |
Name |
Symbol |
|
Factor |
Name |
Symbol |
 |
101 |
deca |
da |
|
101 |
deci |
d |
102 |
hecto |
h |
102 |
centi |
c |
103 |
kilo |
k |
103 |
milli |
m |
106 |
mega |
M |
106 |
micro |
µ |
109 |
giga |
G |
109 |
nano |
n |
1012 |
tera |
T |
1012 |
pico |
p |
1015 |
peta |
P |
1015 |
femto |
f |
1018 |
exa |
E |
1018 |
atto |
a |
1021 |
zetta |
Z |
1021 |
zepto |
z |
1024 |
yotta |
Y |
1024 |
yocto |
y |
 |
- The kilogram
General principles for the writing of unit symbols and numbers were first given by the 9th CGPM (1948, Resolution 7). These were subsequently elaborated by ISO, IEC, and other international bodies. As a consequence, there now exists a general consensus on how unit symbols and names, including prefix symbols and names, as well as quantity symbols should be written and used, and how the values of quantities should be expressed. Compliance with these rules and style conventions, the most important of which are presented in this chapter, supports the readability of scientific and technical papers.
This appendix lists those decisions of the CGPM and the CIPM that bear directly upon definitions of the units of the SI, prefixes defined for use as part of the SI, and conventions for the writing of unit symbols and numbers. It is not a complete list of CGPM and CIPM decisions. For a complete list, reference must be made to the BIPM website, successive volumes of the Comptes Rendus des Séances de la Conférence Générale des Poids et Mesures (CR) and Procès-Verbaux des Séances du Comité International des Poids et Mesures (PV) or, for recent decisions, to Metrologia.
Since the SI is not a static convention, but evolves following developments in the science of measurement, some decisions have been abrogated or modified; others have been clarified by additions. In the SI Brochure, a number of notes have been added by the BIPM to make the text more understandable; they do not form part of the original text.
In the printed brochure, the decisions of the CGPM and CIPM are listed in strict chronological order in order to preserve the continuity with which they were taken. However in order to make it easy to locate decisions related to particular topics a table of contents is also provided, ordered by subject:
Optical radiation is able to cause chemical changes in certain living or non-living materials: this property is called actinism, and radiation capable of causing such changes is referred to as actinic radiation. Actinic radiation has the fundamental characteristic that, at the molecular level, one photon interacts with one molecule to alter or break the molecule into new molecular species. It is therefore possible to define specific photochemical or photobiological quantities in terms of the result of optical radiation on the associated chemical or biological receptors.
In the field of metrology, the only photobiological quantity which has been formally defined for measurement in the SI is for the interaction of light with the human eye in vision. An SI base unit, the candela, has been defined for this important photobiological quantity. Several other photometric quantities with units derived from the candela have also been defined (such as the lumen and the lux, see Table 3 in Chapter 2).
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