An obelus (symbol: ÷, plural: obeli) is a symbol consisting of a short horizontal line with a dot above and below. It is mainly used to represent the mathematical operation of division. It is therefore commonly referred to as the division sign.
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The word "obelus" comes from the Greek word for a sharpened stick, spit, or pointed pillar. This is the same root as that of the word "obelisk". Originally this sign (or a plain line) was used in ancient manuscripts to mark passages that were suspected of being corrupted or spurious.
The obelus, invented by Aristarchus to mark suspected passages in Homer, is frequent in manuscripts of the Gospel to mark just those sections, like the Pericope in John, which modern editors reject. The first corrector of א, probably the contemporary διορθωτής, was at pains to enclose in brackets and mark with dots for deletion two famous passages in Luke written by the original scribe which, being absent from B W 579 and the Egyptian versions, we infer were not accepted in the text at that time dominant in Alexandria, viz. the incident of the "Bloody Sweat" in Gethsemane (Lk.xxi.43 f.) and the saying "Father forgive them" (Lk.xi.34).[1]
The obelus was first used as a symbol for division in 1659 in the algebra book Teutsche Algebra by Johann Rahn. Some think that John Pell, who edited the book, may have been responsible for this use of the symbol. The obelus had been used by some writers to represent subtraction, and that usage continued in some parts of Europe (including Norway and, until fairly recently, Denmark). Unicode has a related character, ⁒, called "commercial minus sign", located at U+2052 (HTML ⁒).
The obelus was used occasionally in Polish language typography to represent ranges (such as the range 1÷10), although this usage has been mostly discontinued. As of 2007, it was also used to indicate a range in Italian documents (for example, 40% ÷ 50% would indicate 40 percent to 50 percent).
The obelus is primarily used as a symbol for division (as on a calculator) and as an operator in elementary arithmetic. Division is also signified in other ways — usually as a fraction: by writing the operands one above the other and separated by a line, or on the same line separated by a solidus or slash.
In many non-Anglophone countries, the colon is used as a division sign: “a divided by b” is written as a : b, and this is widely used to indicate a ratio.
In Microsoft Windows, the obelus is produced with Alt+0247 or Alt+246 on the number pad. In Mac OS, it is produced with Option + / (Option + slash).
On UNIX-based systems using Screen or X with a Compose key enabled, it can be produced by composing : (colon) and - (minus), though this is locale- and setting-dependent. It may also be input by Unicode code-point on GTK-based applications by pressing Control + Shift + U, followed by the codepoint in hexadecimal (F7) and terminated by return.
In the Unicode character set, the obelus is known as the “division sign” and has the code point U+00F7. In HTML, it can be encoded as ÷ or ÷ (at HTML level 3.2), or as ÷.