Overline
Encyclopedia
| description | character | Unicode | HTML |
|---|---|---|---|
| overline | ‾ | U+203E | ‾ ‾ |
| ◌̅ combining |
U+0305 | ̅ | |
| macron | ¯ | U+00AF | ¯ ¯ |
| ◌̄ combining |
U+0304 | ̄ | |
| ˉ spacing |
U+02C9 | ˉ | |
An overline or overbar or overscore (coined in analogy to underline
Underline
An underline, also called an underscore, is one or more horizontal lines immediately below a portion of writing. Single, and occasionally double , underlining was originally used in hand-written or typewritten documents to emphasise text...
and underscore
Underscore
The underscore [ _ ] is a character that originally appeared on the typewriter and was primarily used to underline words...
, attested for mathematical notation since 1899), refers to the typographical feature of a line drawn immediately above the text, for example used to indicate medieval sigla
Sigla
Sigła is a village in the administrative district of Gmina Aleksandrów, within Biłgoraj County, Lublin Voivodeship, in eastern Poland. It lies approximately east of Aleksandrów, south-east of Biłgoraj, and south of the regional capital Lublin....
. Specifically, a line drawn over one symbol is a macron
Macron
A macron, from the Greek , meaning "long", is a diacritic placed above a vowel . It was originally used to mark a long or heavy syllable in Greco-Roman metrics, but now marks a long vowel...
, and a line over a collection of symbols is a vinculum
Vinculum
A vinculum is a horizontal line used in mathematical notation. It may be placed over a mathematical expression to indicate that it is to be considered grouped together, or alternatively it may function as a binary connective between arguments appearing above and below it...
. Marking one or more words with a continuous line above the characters is also described as "overstriking".
In Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
the overline is represented by , and always functions as an independent symbol. The character allows an overline to be placed over any character (as with any combining character
Combining character
In digital typography, combining characters are characters that are intended to modify other characters. The most common combining characters in the Latin script are the combining diacritical marks ....
, it appears over the preceding character: for example, x̅, compared to x‾). A series of overlined characters usually results in an unbroken line, depending on the font (for example, 1̅2̅3̅).
A similar character is (also called "overbar"), and also has a combining variant, , as well as a spacing modifier variant, . The macron characters are shorter than their "overline" counterparts, and a series of macron characters usually do not result in an unbroken line (for example, 1̄2̄3̄). Unlike overline, the macron is present in the ISO/IEC 8859-1
ISO/IEC 8859-1
ISO/IEC 8859-1:1998, Information technology — 8-bit single-byte coded graphic character sets — Part 1: Latin alphabet No. 1, is part of the ISO/IEC 8859 series of ASCII-based standard character encodings, first edition published in 1987. It is informally referred to as Latin-1. It is generally...
and MS-DOS
MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
Codepage 850 encodings. Depending on the context it is used in, the overbar has different meanings. The table to the right gives a summary of the different Unicode characters.
The Unicode character is used to mark in Syriac text a special overline with a dot at each end and the center, stretching from the position of the character to the end of the word. This line traditionally marks abbreviations and numbers. However, most computer systems do not render this line correctly or at all.
Math and science
In mathematics, an overline is used primarily in two situations: either to indicate a line segmentLine segment
In geometry, a line segment is a part of a line that is bounded by two end points, and contains every point on the line between its end points. Examples of line segments include the sides of a triangle or square. More generally, when the end points are both vertices of a polygon, the line segment...
:
or repeating decimal
Repeating decimal
In arithmetic, a decimal representation of a real number is called a repeating decimal if at some point it becomes periodic, that is, if there is some finite sequence of digits that is repeated indefinitely...
value: = 0. = 0.1428571428571428571...
Since it is not always possible to format the number so that the overline is over a certain digit, it is often placed to the left of the digits that repeat:
- 3.¯3 = 3.333333333333...
- 3.12¯34 = 3.123434343434...
The overline is also used to indicate a sample mean:
-
is the average value of 
In set theory
Set theory
Set theory is the branch of mathematics that studies sets, which are collections of objects. Although any type of object can be collected into a set, set theory is applied most often to objects that are relevant to mathematics...
and some electrical engineering
Electrical engineering
Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical...
contexts, negation
Negation
In logic and mathematics, negation, also called logical complement, is an operation on propositions, truth values, or semantic values more generally. Intuitively, the negation of a proposition is true when that proposition is false, and vice versa. In classical logic negation is normally identified...
operators can be written as an overline above the term(s) and/or expression(s) to be negated.
Common set theory notation:
Electrical engineering notation illustrating the saying, "break the line, change the sign":
in which implied multiplication, the times (cross) and the dot all mean logical AND, and the plus sign means logical OR.
In the repetition and negation usages, this notation is also referred to as a vinculum.
The overline notation can indicate a complex conjugate
Complex conjugate
In mathematics, complex conjugates are a pair of complex numbers, both having the same real part, but with imaginary parts of equal magnitude and opposite signs...
and analogous operations.
- if
, then 
In physics, an overline sometimes indicates a vector, although boldface and arrows are also commonly used:
Technical notes
- In HTMLHTMLHyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....
using CSSCascading Style SheetsCascading Style Sheets is a style sheet language used to describe the presentation semantics of a document written in a markup language...
,text - In HTML documents, the macron can be produced with
̄(decimalDecimalThe decimal numeral system has ten as its base. It is the numerical base most widely used by modern civilizations....
̄), and the "combining overline" — with̅(̅). - In TeXTeXTeX is a typesetting system designed and mostly written by Donald Knuth and released in 1978. Within the typesetting system, its name is formatted as ....
, a single symbol can be overlined with\bar xor\bar{x}. Longer sections can be overlined with\overline{ABC}, where a space is written as "\" and an umlaut is written as "\ddot a". - In Microsoft WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
, the ISO/IEC 8859-1]] 0xAF symbol mentioned above can be added in any program with the keystrokes AltAlt- Abbreviations :* Altbier, German beer* Alternate route, a type of highway designation* Alternate character, in online gaming* Alternative rock* Altitude* Altimeter- Acronyms :* Alanine transaminase, a liver enzyme...
+0175 (where numbers are entered from the numeric keypadNumeric keypadA numeric keypad, numpad or tenkey for short, is the small, palm-sized, seventeen key section of a computer keyboard, usually on the very far right. The numeric keypad features digits 0 to 9, addition , subtraction , multiplication and division symbols, a decimal point and Num Lock and Enter keys...
). - In GTKGTK+GTK+ is a cross-platform widget toolkit for creating graphical user interfaces. It is licensed under the terms of the GNU LGPL, allowing both free and proprietary software to use it. It is one of the most popular toolkits for the X Window System, along with Qt.The name GTK+ originates from GTK;...
/GTK+, the symbol can be added using the keystrokes CtrlCTRLCTRL may refer to several things:*Channel Tunnel Rail Link, a high-speed railway line opened in the 2000s in Britain*Control key, an input button present on most computer keyboards*Ctrl, an American comedy web series from NBC...
+ShiftShiftShift generally means to change . Shift may refer to: * Gear shift, to change gears in a car* Shift work, an employment practice* Shift * Shift , a change of level in music...
+U to activate Unicode inputUnicode inputUnicode input is the insertion of a specific Unicode character on a computer. Unicode characters can be inserted in two ways: from the screen by means of an applet from which one can select the character, or by input of the Unicode character from the keyboard...
, then type "00AF" as the code for the character. - In Microsoft WordMicrosoft WordMicrosoft Word is a word processor designed by Microsoft. It was first released in 1983 under the name Multi-Tool Word for Xenix systems. Subsequent versions were later written for several other platforms including IBM PCs running DOS , the Apple Macintosh , the AT&T Unix PC , Atari ST , SCO UNIX,...
, overstriking of text can be accomplished with theEQ \Ofield code. The field code{EQ \O(x,¯)}produces and the field code{EQ \O(xyz,¯¯¯)}produces .
Overstriking of longer sections of text, such as in , can also be produced in many text processors
Word processing
Word processing is the creation of documents using a word processor. It can also refer to advanced shorthand techniques, sometimes used in specialized contexts with a specially modified typewriter.-External links:...
as text markup
Markup language
A markup language is a modern system for annotating a text in a way that is syntactically distinguishable from that text. The idea and terminology evolved from the "marking up" of manuscripts, i.e. the revision instructions by editors, traditionally written with a blue pencil on authors' manuscripts...
as a special form of understriking.
See also
- UnderscoreUnderscoreThe underscore [ _ ] is a character that originally appeared on the typewriter and was primarily used to underline words...
- StrikethroughStrikethroughStrikethrough is a typographical presentation of words with a horizontal line through their center. This is an example....
- UnderlineUnderlineAn underline, also called an underscore, is one or more horizontal lines immediately below a portion of writing. Single, and occasionally double , underlining was originally used in hand-written or typewritten documents to emphasise text...