Overline
An overline, overscore, or overbar, is a typographical feature of a horizontal line drawn immediately above the text.
[1] In Latin, it indicates Roman numerals multiplied by a thousand and it forms medieval abbreviations (sigla).
An overline, that is, a single line above a chunk of text, should not be confused with the macron, a diacritical mark placed above (or sometimes below) individual letters.
[2] In most forms of Latin scribal abbreviation, an overline or macron indicates omitted letters similar to use of apostrophes in English contractions.
Letters with macrons or overlines continue to be used in medical abbreviations in various European languages, particularly for prescriptions.
This is separately encoded in Unicode with the symbols using bar diacritics and appears shorter than other overlines in many fonts.
In the Middle Ages, from the original Indian decimal writing, before printing, an overline over the units digit was used to separate the integral part of a number from its fractional part, as in 9995 (meaning 99.95 in decimal point format).
A similar notation remains in common use as an underbar to superscript digits, especially for monetary values without a decimal separator, as in 9995.
Both illustrate De Morgan's laws and its mnemonic, "break the line, change the sign".
This notation avoids the need for separate tables to convert positive and negative logarithms back to their original numbers.
This goes back to at least the landmark paper published by Nobel prize winners Alan Lloyd Hodgkin and Andrew Fielding Huxley around 1952.
[9] Some Morse code prosigns can be expressed as two or three characters run together, and an overline is often used to signify this.
An overline-like symbol is traditionally used in Syriac text to mark abbreviations and numbers.
X-bar theory makes use of overbar notation to indicate differing levels of syntactic structure.
Some variants of X-bar notation use a double-bar (or double-prime) to represent phrasal-level units.
A series of overlined characters, for example 1̅2̅3̅, may result either in a broken or an unbroken line, depending on the font.
[13] Unicode maps the overline-like character from ISO/IEC 8859-1 and code page 850 to the U+00AF ¯ MACRON symbol mentioned above.
In ChromeOS and Linux, the symbol can be added using the keystrokes Ctrl+⇧ Shift+U to activate Unicode input, then type "00AF" as the code for the character.
The Unicode character U+0B55 ୕ ORIYA SIGN OVERLINE is used as a length mark in Odia script.
The user-interface option is available in their word processors on Linux, macOS and Windows, and also in Android (in tablet format), ChromeOS and iPadOS with Collabora Office.
Collabora Online, Collabora Office and LibreOffice have direct menu support for several styles of Overline in the "Format" menu within applications of their office suites, including spreadsheets, presentations and graphics applications.
The user-interface option is available in the web based suite, and the locally installable applications for Linux, macOS and Windows, and with Collabora Office in Android (in tablet format), ChromeOS and iPadOS.
