Subscript and superscript

A subscript or superscript is a character (such as a number or letter) that is set slightly below or above the normal line of type, respectively. It is usually smaller than the rest of the text. Subscripts appear at or below the baseline, while superscripts are above. Subscripts and superscripts are often used in formulas, mathematical expressions, and specifications of chemical compounds and 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 consistent with the rest of the font, typeface designers make them slightly heavier (i.e. medium or bold typography) than a reduced-size character would be. The vertical distance that sub- or superscripted text is moved from the original baseline varies by typeface and by use.

In typesetting, such types are traditionally called "superior" and "inferior" letters, figures, etc., or just "superiors" and "inferiors". In English, most nontechnical use of superiors is archaic. Superior and inferior figures on the baseline are used for fractions and most other purposes, while lowered inferior figures are needed for chemical and mathematical subscripts.

A single typeface may contain sub- and superscript glyphs at different positions for different uses. The four most common positions are listed here. Because each position is used in different contexts, not all alphanumerics may be available in all positions. For example, subscript letters on the baseline are quite rare, and many typefaces provide only a limited number of superscripted letters. Despite these differences, all reduced-size glyphs go by the same generic terms subscript and superscript, which are synonymous with the terms inferior letter (or number) and superior letter (or number), respectively. Most fonts that contain superscript/subscript will have predetermined size and orientation that is dependent on the design of the font.

Subscripts are used in chemical formulas. For example, the chemical formula for glucose is C₆H₁₂O₆ (meaning that it is a molecule with 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms). The chemical formula of the water molecule, H₂O, indicates that it contains two hydrogen atoms and one oxygen atom.

A subscript is also used to distinguish between different versions of a subatomic particle. Thus electron, muon, and tau neutrinos are denoted ν
_e ν
_μ and ν
_τ. A particle may be distinguished by multiple subscripts, such as Ω⁻
_bbb for the triple bottom omega particle.

Similarly, subscripts are also used frequently in mathematics to define different versions of the same variable: for example, in an equation x₀ and x_f might 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. Commonly, variables with a zero in the subscript are referred to as the variable name followed by "nought" (e.g. v₀ would be read, "v-nought").

Subscripts are often used to refer to members of a mathematical sequence or set or elements of a vector. For example, in the sequence O = (45, −2, 800), O₃ refers to the third member of sequence O, which is 800.