Appendix D
SI Rules for Notation
Symbols for (physical) quantities, be they variables or constants, are given
by a single character (generally Latin or Greek letters) and are printed in
italics, e.g.,F(force),p(pressure),m(chemical potential),k(Boltzmann
constant). Further differentiation is achieved by the use of subscripts and/or
superscripts; these are printed in italics if it concerns the symbol of a
quantity, otherwise in roman type, e.g., cp (specific heat at constant
pressure),h^PP (Planck’s constant),ESD(surface dilational modulus). For
clarity, symbols are generally separated by a (thin) space, e.g.,F¼ma, not
ma. Some generally accepted exceptions occur, such as pH, as well as
symbols (or two letter abbreviations, rather) for the dimensionless ratios
frequently used in process engineering, like Re for Reynolds number and Tr
for Trouton ratio (in roman type).
Symbols for operatorsare given in roman (upright) characters, e.g.,
log, ln, 4 , d (differential), sin. Preferably, they are separated by a thin space
from the quantity symbol, e.g., lnj.
Symbols for unitsare also given in roman type, e.g., m, Pa. Separation
of units is (preferably) by an elevated dot, e.g., Pa?s and kg?m^3 —or by a
space: Pa s and kg m^3 —(but not Pas, etc.). Division is indicated by a
negative sign in the exponent, such as m?s^1 ; m/s is also allowed, but not m/
kg/s, or m/kg s, since these notations are equivocal. Numerical prefixes are
put directly before the main symbol, e.g.,mm, kPa, GV. For compound