## Typographical rules for scientific texts

In scientific texts the visual form of a symbol often implies a semantic meaning which is not easily captured by generic markup. Therefore authors using a generic coding system (such as LaTeX or an XML grammar) need to know about these typographical conventions. The following is a brief summary of the most important rules for composing scientific texts. They are based on two basic international reference texts:

1. SI Unit rules and style conventions
2. International Union of pure and applied Physics. Symbols, Units, Nomenclature and fundamental Constants in Physics. Physica, 146A, pp. 1-67, 1987.
3. D. E. Lowe. A Guide to international recommendations on names and symbols for quantities and on units of measurements. World Health Organization, Geneva, 1975.

The most important rule is consistency: a symbol should always be the same, whether it appears in a formula or in the text, on the main line or as a superscript or subscript. This means, when using (La)TeX, that once you have used a symbol inside mathematics mode (’\$’), you should always use it inside mathematics mode.

Inside math mode, (La)TeX by default prints characters in (math) italics.

In scientific work and by international convention a whole series of symbols must be set in roman (upright) type. In LaTeX, roman inside mathematics mode is achieved with the \mathrm command.

The following families of symbols must always be typeset in roman characters:

• units, such as g, cm, s, keV. Note that physical constants are usually in italics, so units involving constants are mixed roman-italics, e.g., GeV/c (with the c in italic because it symbolizes the speed of light, a constant);
• particle names, for example p, K, q, H;
• names of chemical elements, for example Ne, O, Cu;
• standard mathematical functions (sin, det, cos, tan, Re, Im, etc.). (La)TeX has built-in commands for typesetting these, such as \sin, \log, etc., and you can define new symbols to be treated as operators with the \operatorname command which is defined in the amsmath package that is loaded automatically in the CERN classes);
• names of waves (P-wave), states (R-state), covariant couplings (A for axial, V for vector), (mono)poles (E for electric, M for magnetic);
• abbreviations that are initials of bits of words (exp, for experimental; min, for minimum);
• the d in integrands (e.g., dx).

A nice overview has been prepared by the National Institute of Standards and Technology: Typefaces for symbols in scientific manuscripts.

When, as an author, you follow these rules the reader will understand at first glance what you are talking about. Instances of the importance of using the correct typesetting for symbols are shown in the following table.

e
 roman type italic type A ampere (electric unit) A atomic number (variable) electron (particle name) e electron charge (constant) g gluon (particle name) g gravitational constant l litre (volume unit) l length (variable) m metre (length unit) m mass (variable) p proton (particle name) p momentum (variable) q quark (particle name) q electric charge (variable) s second (time unit) s c.m. energy squared (variable) t tonne (weight unit) t time (variable) V volt (electric unit) V volume (variable) Z Z boson (particle name) Z atomic charge (variable)

Last Mod. 17 November 2006 (MG)