Subscript and superscript

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

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Example of subscripts and superscripts. In each example the first "2" is a professionally designed subscript included as part of the glyph set; the second "2" is a manual approximation using a small version of the standard "2." Notice that the visual weight of the first "2" matches the other letters better. (The top typeface is Adobe Garamond Pro; the size of the subscript is about 62% of the original characters, dropped by about 16%. The second typeface is Myriad Pro; the superscript is about 60% of the original characters, raised by about 44%.)

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, an 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%–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.)

The terms subscript and superscript are synonymous with the terms inferior letter and superior letter, respectively.

[edit] Uses

[edit] 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 6 carbon atoms, 12 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.

Also in mathematics and computing, subscript can be used to represent the radix, or base, of a written number, especially where multiple bases are used alongside each other. For example, comparing values in hexadecimal, denary, and octal one might write C_hex = 12_dec = 14_oct.

[edit] Superscripts

See also: superior letter

In mathematics, superscripts are used to raise one number or variable to the power of another number or variable. Thus y⁴ is y raised to the fourth power, and the famous equation E = mc² includes a term for the speed of light squared.

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

Ordinal indicators are sometimes written as superscripts (1^st, 2^nd, 3^rd rather than 1st, 2nd, 3rd), although many English-language style guides recommend against this use.

Many abbreviations use superscripts, especially historically. Examples in English include J^os (for Joseph), th^t or y^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, Failed to parse (Missing texvc executable; please see math/README to configure.): \mathrm{U}^{238}_{92}

is an atom of uranium with 92 protons and 238 nucleons.

[edit] Software support

[edit] Desktop publishing

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 raise or lower it by 33%; 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 native OpenType 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, below.

[edit] HTML

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.

[edit] TeX

In TeX's mathematics mode (as used in MediaWiki), subscripts are typeset with the underscore, while superscripts are made with the caret. Thus $X_{ab}$ produces Failed to parse (Missing texvc executable; please see math/README to configure.): X_{ab} , and $X^{ab}$ produces Failed to parse (Missing texvc executable; please see math/README to configure.): X^{ab} .

[edit] Unicode

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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

[edit] OpenType

One of the advanced features of OpenType typefaces is support for professionally designed subscript and superscript glyphs. Exactly which glyphs are included varies by typeface; some have only basic support for numerals, while others contain a full set of letters, numerals, and punctuation. Since many of these glyphs are not included in Unicode, they are typically placed in the Unicode Private Use Area.

[edit] See also

• mathematical notation
• Superior letter
• typesetting
• font

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