Typefaces for Symbols in Scientific…

                           Typefaces for Symbols in Scientific Manuscripts
     Most word processing software now in use at NIST is capable of producing lightface (that is, regular) or boldface letters of
the Latin or Greek alphabets in both roman (upright) and italic (sloping) types. The understandability of typed and typeset
scientific and technical publications is facilitated if symbols are in the correct typeface. The following rules are taken from
International Organization for Standardization (ISO) International Standard ISO 31-0:1992 to ISO 31-13:1992.
     The typeface in which a symbol appears helps to define what the symbol represents. For example, irrespective of the typeface
used in the surrounding text, "A" would be typed or typeset in
                  -- italic type for the scalar quantity area:        A;
                  -- roman type for the unit ampere:           A;
                  -- italic boldface for the vector quantity vector potential:           A.

More specifically, the three major categories of symbols found in scientific and technical publications should be typed or typeset
in either italic or roman type, as follows:
                  -- symbols for quantities and variables : italic;
                  -- symbols for units : roman;
                  -- symbols for descriptive terms : roman.

These rules imply that a subscript or superscript on a quantity symbol is in roman type if it is descriptive (for example, if it is a
number or represents the name of a person or a particle); but it is in italic type if it represents a quantity, or is a variable such as
x in E x or an index such as i in i x i that represents a number. An index that represents a number is also called a "running number."
The following four sections give examples of the proper typefaces for these three major categories.

Quantities and variables -- italic
     Symbols for quantities are italic, as are symbols for functions in general, for example, f (x ):

          t=3s              t time, s second                              T = 22 K        T temperature, K kelvin
          r = 11 cm         r radius, cm centimeter                        = 633 nm              wavelength, nm nanometer

Constants are usually physical quantities and thus their symbols are italic; however, in general, symbols used as subscripts and
superscripts are roman if descriptive:

          NA       Avogadro constant, A Avogadro                          R molar gas constant
              D    Debye temperature, D Debye                             Z  atomic number
          e        elementary charge                                      me m mass, e electron

Running numbers and symbols for variables in mathematical equations are italic, as are symbols for parameters such as a and b
that may be considered constant in a given context:
                                   m
                              y=         xi zi                               x 2 = ay 2 + bz 2
                                   i=1

Symbols for vectors are boldface italic, symbols for tensors are sans-serif bold italic, and symbols for matrices are boldface italic:
                                                                                              a11 a12
          A B=C           (vectors)                  T        (tensors)              A=                  (matrices)
                                                                                              a21 a22

Symbols used as subscripts and superscripts are italic if they represent quantities or variables:
          cp      p pressure                     qm m mass                                solid angle                 z   z   z coordinate

Units -- roman
     The symbols for units and SI prefixes are roman:
          m         meter                             g         gram                              L     liter
          cm        centimeter                            g     microgram                         mL    milliliter
                                                                                                                                             (over)
Descriptive terms -- roman
     Symbols representing purely descriptive terms (for example, the chemical elements) are roman, as are symbols representing
mathematical constants that never change (for example, ) and symbols representing explicitly defined functions or well defined
operators (for example, (x ) or div):
Chemical elements:
    Ar             argon                                              B        boron                                C       carbon

Mathematical constants, functions, and operators:
    e               base of natural logarithms                  xi                        sum of                 ln x       loge           natural logarithm of
    exp x           exp exponential of                        sin x            sin        sine of                lg x       log10          common (decimal)
                                                                                                                                           logarithm of
    d x /dt d 1st derivative of                               log a x          log a      logarithm to the       lb x       log2           binary logarithm of
                                                                                          base a of
Symbols used as subscripts and superscripts are roman if descriptive:
        (ir)
        0           ir irrational                                     Ek        k kinetic
     l
    Vm              m molar, l liquid phase                                B    B Bohr

Sample equations showing correct type
                   q1 q2
    F=                                                                F = ma                                        pV = nRT
               4      0    r2

        B
                    *           *
            = x B V m,B / x A V m, A                                  Ea = RT 2 d(ln k )/dT                         c1 =        ­5
                                                                                                                                     /[exp(c 2 / T ) ­1]

                                                                                                                    F
    E = mc 2                                                          pB =
                                                                      ~          B   lim (xB p /         B   )        = ­ grad V
                                                                                     p0                             Q
Greek alphabet in roman and italic type
    The following table shows the proper form, in both roman and italic type, of the upper-case and lower-case letters of the
Greek alphabet.
                     Greek alphabet in roman and italic type

                                alpha                                 A                                                 A
                                beta                                  B                                                 B
                                gamma
                                delta
                                epsilon                               E                    ,                            E                       ,
                                zeta                                  Z                                                 Z
                                eta                                   H                                                 H
                                                                               (a)                 (b)                               (a)             (b)
                                theta                                      ,                  ,                             ,                   ,
                                iota                                  I
                                                                                                   (b)                                               (b)
                                kappa                                 K                        ,                                                ,
                                lambda
                                mu                                    M                                                 M
                                nu                                    N                                                 N
                                xi
                                omicron                               O                   o                             O                   o
                                pi                                                             ,                                                 ,
                                                                                                   (b)                                               (b)
                                rho                                   P                       ,                         P                       ,
                                sigma
                                tau                                   T                                                 T
                                upsilon
                                phi                                                           ,                                                 ,
                                chi
                                psi
                                omega
                     (a)
                         The International Organization for Standardization (ISO) gives only the first of these two letters (see ISO International
                     Standard ISO 31-0:1992).
                     (b)
                         ISO gives these two letters in the reverse order (see ISO International Standard ISO 31-0:1992).