




NonSI units accepted for use with the SI, and units based on fundamental constants (contd.)


Table 9 differs from Table 8 only in that the units in Table 9 are related to the older CGS (centimetregramsecond) system of units, including the CGS electrical units. In the field of mechanics, the CGS system of units was built upon three quantities and their corresponding base units: the centimetre, the gram, and the second. The CGS electrical units were still derived from only these same three base units, using defining equations different from those used for the SI. Because this can be done in different ways, it led to the establishment of several different systems, namely the CGSESU (electrostatic), the CGSEMU (electromagnetic), and the CGSGaussian unit systems. It has always been recognized that the CGSGaussian system, in particular, has advantages in certain areas of physics, particularly in classical and relativistic electrodynamics (9th CGPM, 1948, Resolution 6). Table 9 gives the relations between these CGS units and the SI, and lists those CGS units that were assigned special names. As for the units in Table 8, the SI prefixes are used with several of these units (e.g. millidyne, mdyn; milligauss, mG, etc.).
Table 9. NonSI units associated with the CGS and the CGSGaussian system of units

Quantity 
Name of unit 
Symbol for unit 
Value in SI units 

energy 
erg ^{(a)} 
erg 
1 erg = 10^{–7} J 
force 
dyne ^{(a)} 
dyn 
1 dyn = 10^{–5} N 
dynamic viscosity 
poise ^{(a)} 
P 
1 P = 1 dyn s cm^{–2} = 0.1 Pa s 
kinematic viscosity 
stokes 
St 
1 St = 1 cm^{2} s^{–1} = 10^{–4} m^{2} s^{–1} 
luminance 
stilb ^{(a)} 
sb 
1 sb = 1 cd cm^{–2} = 10^{4} cd m^{–2} 
illuminance 
phot 
ph 
1 ph = 1 cd sr cm^{–2} = 10^{4} lx 
acceleration 
gal ^{(b)} 
Gal 
1 Gal = 1 cm s^{–2} = 10^{–2} m s^{–2} 
magnetic flux 
maxwell ^{(c)} 
Mx 
1 Mx = 1 G cm^{2} = 10^{–8} Wb 
magnetic flux density 
gauss ^{(c)} 
G 
1 G = 1 Mx cm^{–2} = 10^{–4} T 
magnetic field 
œrsted ^{(c)} 
Oe 
1 Oe (10^{3}/4) A m^{–1} 
(a) 
This unit and its symbol were included in Resolution 7 of the 9th CGPM (1948). 
(b) 
The gal is a special unit of acceleration employed in geodesy and geophysics to express acceleration due to gravity. 
(c) 
These units are part of the socalled "electromagnetic" threedimensional CGS system based on unrationalized quantity equations, and must be compared with care to the corresponding unit of the International System which is based on rationalized equations involving four dimensions and four quantities for electromagnetic theory. The magnetic flux, , and the magnetic flux density, B, are defined by similar equations in the CGS system and the SI, so that the corresponding units can be related as in the table. However, the unrationalized magnetic field, H (unrationalized) = 4 x H (rationalized). The equivalence symbol is used to indicate that when H (unrationalized) = 1 Oe, H (rationalized) = (10^{3}/4) A m^{–1}. 





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

Factor 
Name 
Symbol 

Factor 
Name 
Symbol 

10^{1} 
deca 
da 

10^{–1} 
deci 
d 
10^{2} 
hecto 
h 
10^{–2} 
centi 
c 
10^{3} 
kilo 
k 
10^{–3} 
milli 
m 
10^{6} 
mega 
M 
10^{–6} 
micro 
µ 
10^{9} 
giga 
G 
10^{–9} 
nano 
n 
10^{12} 
tera 
T 
10^{–12} 
pico 
p 
10^{15} 
peta 
P 
10^{–15} 
femto 
f 
10^{18} 
exa 
E 
10^{–18} 
atto 
a 
10^{21} 
zetta 
Z 
10^{–21} 
zepto 
z 
10^{24} 
yotta 
Y 
10^{–24} 
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 ProcèsVerbaux 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 nonliving 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).





