Subscript and superscript

This article is about the terms 'subscript' and 'superscript' as used in typography. "SuperScript" can also refer to a commercially available Reverse transcriptase.

A subscript or superscript is a number, figure, symbol, or indicator that appears smaller than the normal line of type and is set slightly below or above it – subscripts appear below the baseline, while superscripts are above. Subscripts and superscripts are typically used in formulas, mathematical expressions, and descriptions of chemical compounds or isotopes, but have many other uses as well.

In professional typography, subscript and superscript characters are not simply ordinary characters reduced in size; to keep them visually similar to the rest of the font, typeface designers make them slightly heavier than a reduced-size character would be. Likewise, the amount that sub- or superscripted text is moved from the original baseline varies by typeface. However, a good approximation to professional appearance can be obtained by using regular characters reduced to 58–67% of their original size. For subscripts, they are dropped below the baseline by about 10–20% of the original font size; for superscripts they are raised by about 30% to 40% of the nominal font size. (So for 12-point type, a good chemical subscript might be 7 or 8 points in size, dropped between 1.5 and 2.5 points. The best values will depend on the typeface.)

Uses

Subscripts

Perhaps the most familiar example of subscripts is in chemical formulas. For example, the formula for glucose is C₆H₁₂O₆, meaning that it is a molecule with six carbon atoms, twelve hydrogen atoms and six oxygen atoms.

Subscripts are also used frequently in mathematics to define different versions of the same variable; for example, in an equation x₀ and x_f may indicate the initial and final value of x, while v_rocket and v_observer would stand for the velocities of a rocket and an observer, respectively.

Superscripts

See also: superior letter

In mathematics, superscripts are used to raise one number or variable to the power of another number of variable. y⁴ is y raised to the fourth power.

Superscripts can be used to indicate the presence of a footnote in a document, like this⁵ or this^xi.

Sometimes, ordinal endings for numbers are written as superscripts (1^st, 2^nd, 3^rd rather than 1st, 2nd, 3rd).

Many abbreviations use superscripts, especially historically. Examples in English include J^os (for Joseph), th^t (for that), and y^e (for the, originally þe), or in French M^lle (for Mademoiselle) and G^le (for générale).

Atomic isotopes are written using superscripts. In symbolic form, the number of nucleons is denoted as a superscripted prefix to the chemical symbol (e.g. ³He, ¹²C, ¹³C, ¹³¹I and ²³⁸U).

Subscripts and superscripts can also be used to give specific information about atomic nucleons. For example, $\mathrm {U} _{92}^{238}$ is an atom of uranium with 92 protons and 238 nucleons.

Software Support

HTML subscripts and superscripts
A_b C^d

In HTML and Wiki syntax, subscript text is produced by putting it inside the tags <sub> and </sub>. Similarly, superscripts are produced with <sup> and </sup>. The exact size and position of the resulting characters will vary by font and browser, but are usually reduced to around 75% original size.

Many text editing and word processing programs have automatic subscripting and superscripting features, although these programs usually simply use ordinary characters reduced in size and moved up or down – they are not true subscript or superscript glyphs. The default values for OpenOffice, for example, reduce the type to 58% of the original size and drop it by 10% (for subscripts) or raise it by 33% (for superscripts); these values can also be set manually.

Professional typesetting programs such as QuarkXPress or Adobe InDesign also have similar features for automatically converting regular type to subscript or superscript. These programs, however, may also offer offer support for the special subscript and superscript glyphs included in many professional typeface packages (such as those shown in the image above). See also OpenType.

In TeX's math mode (as used in MediaWiki), subscripts are typeset with the underscore, while superscripts are made with the caret. Thus $X_{ab}$ produces $X_{ab}$ , and $X^{ab}$ produces $X^{ab}$ .

File:Sub super num dem.png

The difference between subscript/superscript and numerator/denominator glyphs. The typeface is Myriad Pro.

Unicode U+2070 to U+209F defines subscript and superscript characters 0 through 9 as well as +, −, =, (, and ). Additionally, the characters a, e, o, x, and ə are available as subscripts, and i and n are available as superscripts. Note, however, that most fonts which include these characters use them for mathematical numerator and denominator glyphs, which are the same size and weight as subscripts and superscripts but are aligned with the baseline or cap line (see image at right). For details and examples, see Unicode subscripts and superscripts.

Unicode also includes other characters which are superscripted:

in Latin-1 Supplement block, the feminine and masculine ordinal indicators U+00AA ª, U+00BA º and superscript numerals U+00B9 ¹, U+00B2 ², U+00B3 ³
in the Spacing Modifier Letters block, U+02B0 to U+02B8, ʰ ʱ ʲ ʳ ʴ ʵ ʶ ʷ ʸ, U+02E2 ˢ, U+02E3 ˣ
in the Phonetic Extensions block, U+1D43 to U+1D61, ᵃ ᵄ ᵅ ᵆ ᵇ ᵈ ᵉ ᵊ ᵋ ᵌ ᵍ ᵎ ᵏ ᵐ ᵑ ᵒ ᵓ ᵔ ᵕ ᵖ ᵗ ᵘ ᵙ ᵚ ᵛ ᵜ ᵝ ᵞ ᵟ ᵠ ᵡ