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

METRICATION 453 UNITS TO BE ALLOWED IN CONJUNCTION WITH SI physical name symbol definition quantity of unit for unit of unit length parsec pc 30.87 X 10 •5 m area barn b 10 -28 m 2 hectare ha 104 m 2 volume litre 1 10 -3 m 3 pressure bar bar 105 N m -2 mass tonne t 103 kg ----- 1 Mg kinematic viscosity stokes St 10 -4 m 2 s -• diffusion coefficient dynamic viscosity poise P 10 -• kg m -• s -• magnetic flux density gauss G 10 -4 T (magnetic induction) radioactivity curie Ci 37 X 109 s -• energy electronvolt eV 1.6021 X 10 -•9 J The common units of time [e.g. hour (h), year] will persist, and also, in appropriate contexts, the angular degree. Until such time as a new name may be adopted for the kilogramme as the basic unit of mass, the gramme will often be used, both as an elementary unit (to avoid the absurdity of mkg) and in association with numerical prefixes, e.g. •g. EXAMPLES OF UNITS CONTRARY TO SI, WITH THEIR EQUIVALENTS* physical quantity length area volume unit equivalent Kngstr6m 10 -•ø m inch 0.0254 m foot 0.3048 m yard 0.9144 m square inch 645.16 mm 2 square foot 0.092 903 m 2 square yard 0.836 127 m21 cubic inch 1.638 71 X 10 -5 m 3 cubic foot 0.028 316 8 m 3 U.K. gallon 0.004 546 092 m 3 U.S. gallon 0.003 785 41 m 3 fluid ounce 28.413 1 cm 3 Fuller lists are to be found in Anderton, P. and Bigg, P. H. Changing to the metric sy.stem. 2rid edn. (1967). (H.M. Stationery Office, London.)