METRICATION 451 BASIC SI UNITS physical name quantity of unit length metre mass kilogramme time second electric current ampere thermodynamic temperature degree Kelvin luminous intensity candela Symbols for units do not take a plural form. symbol for unit m kg s A *K cd SUPPLEMENTARY UNITS These units are dimensionless. physical quantity plane angle solid angle name of unit radian steradian symbol for unit rad sr DERIVED SI UNITS WITH SPECIAL NAMES physical name symbol quantity of unit for unit energy joule J force newton N power watt W electric charge coulomb C electric potential volt V difference electric resistance ohm fl electric capacitance farad F magnetic flux weber Wb inductance henry H magnetic flux density tesla T luminous flux lumen lm illumination lux lx frequency hertz Hz customary temperature, t degree Celsius øC definition of unit kg m 2 s -2 kgms -2 = Jm-' kg m 2 s -3 ---- J s -x As kgm 2s -3A-' •- JA-'s -• kgm 2s -3A -2= VA -• A 2 s 4 kg-' m -2 ---- A s V -• kg m 2 s -2 A-' ---- V s kg m 2 s -2 A -2 -• V s A -• kg s -2 A-' ---- V s m -2 cd sr cd sr m -2 cycle per second t/øC = T/øK--273.15

452 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS FRACTIONS AND MULTIPLES fraction prefix symbol multiple prefix symbol I 10 -1 deci d 10 deka da I 10 -2 centi c 10 2 hecto h 10 -3 milli m 10 3 kilo lc 10- * micro • 10 6 mega • [ 10 -• nano n 10 • giga G 10 -•2 pico p 10 • 2 tera T 1 O- • s femto f 10 -• atto a * To be restricted to instances where there is a strongly felt need, such as may be ex- perienced in the early days of metrication in fayour of the centim-•tre as the unit of length in certain biological measurements. by Compound prefixes should not be used, e.g. 10 '9 newton is represented 1 nN, not 1 mpN. The attaching of a prefix to a unit in effect constitutes a new unit, e.g. 1 kN 2 = 1 (kN) 2 = 106N 2 not I k(N 2) .... 10•N 2. Where possible any numerical prefix should appear in the numerator of an expression. EXAMPLES OF OTHER DERIVED SI UNITS physical quanti(¾ area volume density velocity angular velocity acceleration pressure kinematic viscosity, diffusion coefficient dynamic viscosity electric field strength magnetic field strength luminanee symbol SI unit for unit square metre m 2 cubic metre m 3 kilogramme per cubic metre kg m- • metre per second m s -• radian per second rad s -• ,netre per second squared ,n s -2 newton per square metre N m -2 square metre per second nl 2 s -• newton second per square metre N s m -2 volt per metre V m -• ampere per metre A m -• candela per square mvtre mcd -2