View source for Slashed zero

{{short description|Glyph variant of numeral 0 (zero) with slash}}
{{other uses|∅ (disambiguation)}}
[[Image:SlashedZeros.svg|250px|thumb|right|class=skin-invert-image|Display of zero in three typefaces, from top to bottom: slashed zero, dotted zero, plain or open zero]]

The '''slashed zero''', [[Image:SlashedZeros (cropped).svg|x12px|class=skin-invert]], is a representation of the Arabic digit zero ("0") with a slash through it. This variant zero glyph is often used to distinguish the digit zero from the Latin script letter O anywhere that the distinction needs emphasis, particularly in encoding systems, scientific and engineering applications, [[Computer programming|computer programming]] (such as [[Software development|software development]]), and telecommunications. It thus helps to differentiate characters that would otherwise be [[Homoglyph|homoglyph]]s. It was commonly used during the [[Engineering:Punched card|punch card]] era, when programs were typically written out by hand, to avoid ambiguity when the character was later typed on a card punch.

==Usage==
[[File:Postalete TCB. 01-20.jpg|thumb|right|Slashed zeroes on a bus stop sign in Portugal, 2020]]
The slashed zero is used in a number of fields in order to avoid confusion with the letter "O". It is used by computer programmers, in recording amateur radio call signs and in military radio, as logs of such contacts tend to contain both letters and numerals.

The slashed zero was used on teleprinter circuits for weather applications. In this usage it was sometimes called communications zero.<ref>{{cite book |title=Reference Data for Radio Engineers |edition=Fifth |publisher=Howard W. Sams & Co. Inc. |year=1970 |pages=30–38 |id=Table&nbsp;23}}</ref>

The slashed zero can be used in [[Chemistry:Stoichiometry|stoichiometry]] to avoid confusion with the symbol for [[Chemistry:Oxygen|oxygen]] (capital O).

The slashed zero is also used in charting and documenting in the medical and healthcare fields to avoid confusion with the letter "O". It also denotes an absence of something (similar to the usage of an "[[Empty set|empty set]]" character), such as a sign or a symptom.

Slashed zeros are used on New Zealand number plates.<ref>
{{cite web
 |title=PA NZEA
 |website=World License Plates (worldlicenseplates.com)
 |url=http://www.worldlicenseplates.com/world/PA_NZEA.html
}}
</ref>

==History==
The slashed zero predates computers, and is known to have been used in the twelfth and thirteenth centuries.{{sfn|Cajori|1928|p=51}}

In the days of the typewriter, there was no key for the slashed zero. Typists could generate it by first typing either an uppercase "O" or a zero and then backspace, followed by typing the slash key. The result would look very much like a slashed zero.

It is used in many [[Baudot code|Baudot]] [[Engineering:Teleprinter|teleprinter]] applications, specifically the keytop and typepallet that combines "P" and slashed zero.<ref name=Teletype-1948-04-Bul-1164B/> Additionally, the slashed zero is used in many [[ASCII]] graphic sets descended from the default typewheel on the [[Engineering:Teletype Model 33|Teletype Model 33]].<ref name=Teletype-Bul-1184B/>

The use of the slashed zero by many computer systems of the 1970s and 1980s inspired the 1980s space rock band Underground Zerø to use a heavy metal umlaut Scandinavian vowel ''ø'' in the band's name and as the band logo on all their album covers.

Along with the Westminster, MICR, and [[OCR-A]] fonts, the slashed zero became one of the things associated with [[Social:Hacker culture|hacker culture]] in the 1980s. Some cartoons depicted computer users talking in [[Binary code|binary code]] with 1s and 0s using a ''slashed zero'' for the 0.

Slashed zeroes have been used in the [[Software:Adobe Flash|Flash-based]] artwork of Young-Hae Chang Heavy Industries, notably in their 2003 work, ''Operation Nukorea''. The reason for their use is unknown, but has been conjectured to be related to themes of "negation, erasure, and absence".<ref name=Greenfield-2013-04-13-piano/>

==Similar symbols==
The slashed zero has the disadvantage that it can be confused with several other symbols. See the disambiguation page for the symbol Ø for a comprehensive listing.

==Representation in Unicode and HTML==

{| class="wikitable"
|+ Unicode representation
|-
! Glyph !! Variation sequence !! HTML !! Description of appearance 
|-
| {{char|0&#xFE00;}} || 0030 FE00 || 0&amp;#xFE00; || short diagonal stroke form of DIGIT ZERO
|}

In [[Unicode]], slashed zero is considered a standardized typographic variation of the [[Arabic numerals|Arabic digit]] zero {{char|0}}, which is code point {{tt|U+0030}}. Appending Variation Selector 1 {{tt|U+FE00}} after the zero creates the "short diagonal stroked form",<ref name=unicodevariants>{{cite web |url=http://unicode.org/Public/UNIDATA/StandardizedVariants.txt |title=Standardized Variants |publisher=Unicode, Inc. |access-date=2017-03-01 |url-status=live |archive-url=https://web.archive.org/web/20161221025841/http://www.unicode.org/Public/UNIDATA/StandardizedVariants.txt |archive-date=21 December 2016 }}</ref> on this browser it produces {{char|0&#xFE00;}}.

Note that the above should not be confused with the "slashed zero variant of the [[Empty set|empty set]]", <math>\emptyset</math>, as popularized by Donald Knuth's [[Software:TeX|TeX]].<ref name="emptyset">{{cite web |last1=Beeton |first1=Barbara |last2=Freytag |first2=Asmus |last3=Iancu |first3=Laurențiu |last4=Sargent |first4=Murray |title=Proposal to Represent the Slashed Zero Variant of Empty Set |url=http://www.unicode.org/L2/L2015/15268-slashed-zero.pdf |access-date=23 January 2025}}</ref> Unicode represents that character as the empty set (&emptyset;) with variation selector 1.<ref name="unicodevariants" />

Prior to Unicode 9.0, there was no [[Code point|code point]] defined for altering the visual appearance of zero. This meant that the slashed zero [[Glyph|glyph]] was displayed for {{tt|U+0030}} only—''and then always''—in fonts whose designer chose the option. Successful display on a particular local system depended on making sure that such a font was available — either via the system's font files or via [[Font embedding|font embedding]] — and selected. (See also, [[Slashed zero#Combining solidus|Combining solidus]] below.)

In [[HTML]], slashed zero can be enabled by using [[CSS]] property <syntaxhighlight lang=css inline>font-variant-numeric: slashed-zero</syntaxhighlight> or alternatively <syntaxhighlight lang=css inline>font-feature-settings: 'zero'</syntaxhighlight>. If the font has support for [[OpenType]] feature tag <code>zero</code>, slashed zero will be substituted.<ref>{{cite web |url=https://developer.mozilla.org/en-US/docs/Web/CSS/font-variant-numeric |title=font-variant-numeric |website=MDN Web Docs |access-date=2025-02-21 }}</ref><ref>{{cite web |url=https://developer.mozilla.org/en-US/docs/Web/CSS/font-feature-settings |title=font-feature-settings |website=MDN Web Docs |access-date=2025-02-21 }}</ref><ref>{{cite web |url=https://learn.microsoft.com/en-us/typography/opentype/spec/features_uz |title=Registered Features: Descriptions and Implementations (u – z) |website=Microsoft Learn |access-date=2025-02-21 }}</ref>

==Typography==
[[Image:Deutsches Kfz-Kennzeichen für Behördenfahrzeuge (Nummernbereich 3).jpg |German license plate depicting diagonal gap|thumb|right]]
In most typographic designs, the slash of a slashed zero usually does not extend past the ellipse. This contrasts with the Scandinavian vowel "Ø", the [[Empty set|empty set]] symbol "∅", and the diameter symbol "⌀". Conversely, Japanese typefaces frequently render slashed zero with the slash extending beyond the ellipse.<ref>{{cite web |last1=Lunde |first1=Ken |title=Proposal to add standardized variation sequence for U+FF10 FULLWIDTH DIGIT ZERO |url=https://www.unicode.org/L2/L2017/17294-fullwidth-slashed-zero.pdf |publisher=International Organization for Standardization |access-date=6 September 2025 |date=2017-08-14}}</ref>

A convention common on early line printers left zero unornamented but added a tail or hook to the letter-O so that it resembled an inverted [[Software:Q|Q]] (like U+213A ℺) or cursive capital letter-O (<math>\,\mathcal{O} \,</math>).<ref name=Bemer-1967-08-ACM/>

In the [[Fixedsys]] typeface, the numeral 0 has two internal barbs along the lines of the slash. This appears much like a white "S" within the black borders of the zero.

In the FE-Schrift typeface, used on German car license plates, the zero is rectangular and has an "insinuated" slash: a diagonal crack just beneath the top right curve.

==Typefaces==

[[Typeface]]s commonly found on personal computers that use the slashed zero include:

* [[Terminal (typeface)|Terminal]] in [[Company:Microsoft|Microsoft]]'s [[Software:Windows|Windows]] line.
* [[Consolas]] in [[Company:Microsoft|Microsoft]]'s [[Software:Windows Vista|Windows Vista]], [[Software:Windows 7|Windows 7]], [[Software:Microsoft Office 2007|Microsoft Office 2007]] and [[Software:Visual Studio|Microsoft Visual Studio 2010]]
* [[Menlo (typeface)|Menlo]] in [[Software:MacOS|macOS]]
* [[Monaco (typeface)|Monaco]] in [[Software:MacOS|macOS]]
* [[San Francisco (sans-serif typeface)|SF Mono]] in [[Software:MacOS|macOS]]<ref name=AppleInc-c2017-fonts/><ref name=Nowell-67681-DsgnrNws/>
* The [[Software:Fedora (operating system)|Fedora]] Linux distribution ships with a tweaked variant of the Liberation typeface which adds a slash to the zero; this is not present on most other Linux distributions.
* [[ProFont]]
* [[Roboto]] Mono

Dotted zero typefaces:

* The [[DejaVu fonts|DejaVu]] family of typefaces has a "DejaVu Sans Mono" variant with a dotted zero.<ref>{{cite web |url= http://sixrevisions.com/web_design/a-web-designers-guide-to-linux-fonts/ |title= A Web Designer's Guide to Linux Fonts |first= Michael |last= Tuck |date= 2010-08-03 |work= Six Revisions |url-status= live |archive-url= https://web.archive.org/web/20120616171124/http://sixrevisions.com/web_design/a-web-designers-guide-to-linux-fonts/ |archive-date= 16 June 2012 }}</ref>
*[[Andalé Mono]] has a dotted zero.
*[[IBM Plex|IBM Plex Mono]] uses a dotted zero.
*[[Source Code Pro]] and its associated typefaces use a dotted zero.
*[[Cascadia Code]], the default font for [[Software:Windows Terminal|Windows Terminal]], [[Software:Visual Studio|Visual Studio]], and [[Software:Visual Studio Code|Visual Studio Code]], uses a dotted zero.<ref>{{cite web |url=https://github.com/microsoft/cascadia-code/blob/main/images/cascadia-code-characters.png |title= Cascadia Code character set|website= [[GitHub]]}}</ref>

==Variations==

===Dotted zero===
{{SpecialChars}}
The zero with a dot in the center seems to have originated as an option on [[Engineering:IBM 3270|IBM 3270]] display controllers. The dotted zero may appear similar to the Greek letter [[Biology:Theta|theta]] (particularly capital theta, Θ), but the two have different glyphs. In [[Raster graphics|raster]] fonts, the theta usually has a horizontal line connecting, or nearly touching, the sides of an O, while the dotted zero simply has a dot in the middle. However, on a low-definition display, such a form can be confused with a numeral 8. In some fonts the IPA letter for a bilabial click (ʘ) looks similar to the dotted zero.

Alternatively, the dot can become a vertical trace—for example, by adding a "combining short vertical line overlay" <code>(U+20D3)</code>. It may be coded as <code><nowiki>0&amp;#x20D3;</nowiki></code> giving <span style="font-family:Code2000" class="Unicode">0⃓</span>.

The dotted zero has been used on the vehicle registration plates of Slovakia since 2023.<ref name="sampleSlovakLicencePlates">[https://www.minv.sk/?vzory-tabuliek-s-evidencnym-cislom-pridelovane-na-vozidla] Official templates of Slovak license plates (in Slovak)</ref>

===Slashed letter 'O'===
[[File:Apollo_11_video_console.jpg|thumb|[[Apollo 11]] video display terminal with a slashed O]]
[[Company:IBM|IBM]] (and a few other early mainframe makers) used a convention in which the letter O had a slash and the digit 0 did not.<ref name=Dartmouth-1964-10-01-BASIC/> This is even more problematic for Danes, Faroese, and Norwegians because it means two of their letters — the O and slashed O (Ø) — are visually similar.


===Combining solidus===
Before [[Unicode]] standardized the slashed variation of zero (0&#xFE00;) seen above, it did allow [[Unicode#Ready-made versus composite characters|composite characters]] which were used historically to obtain a crude typographic approximation where a slash is drawn upon a zero. It is treated literally as "a zero that is slashed", and it is [[Character encoding|coded]] as two characters: a standard zero {{char|0}} followed by either "combining short solidus overlay" {{tt|U+0337}} or "combining long solidus overlay" {{tt|U+0338}}. However, besides confusing the meaning of the digit zero, it will make a mess if the zero is already slashed in the font. There is no way to specify an unslashed zero that can always be safely overprinted. Laying a slash over letter O also risks wrong appearance and confusion. 

For example, placing the "long solidus", which may be written in [[HTML]] as {{code|0&#x338;}}, appears as {{char|0&#x338;}}. Using the "short solidus overlay" {{tt|U+0337}} after a standard zero character is coded as {{code|0&#x337;}} and produces the following: {{char|0&#x337;}}. 

{| class="wikitable"
|+ The obsolete and wrong way 
|-
! Method !! Glyph !! Notes
|-
| Zero, Combining short solidus overlay || 0̷ || Do not do this, use 0&#xFE00; instead
|-
| Zero, Combining long solidus overlay || 0̸ || Do not do this
|-
| Letter 'o', short solidus || o̷ || Do not do this, could be confused for ø or [[Diameter#Symbol|⌀]] 
|-
| Letter 'O', long solidus || O̸ || Do not do this, could be confused for Ø or [[Empty set|∅]]
|}

===Reversed slash===
Some [[Company:Burroughs Corporation|Burroughs]]/[[Company:Unisys|Unisys]] equipment displays a zero with a reversed slash, similar to the [[No symbol|no symbol]], {{char|🛇}}, as does the free typeface Atkinson Hyperlegible.

==See also==
*[[0 (number)|0 (number)]]
*{{annotated link|Symbols for zero}}
*[[Names for the number 0 in English]]
*{{slink|Arabic numeral variations|Slashed zero}}
*{{slink|Regional handwriting variation|Arabic numerals}}

==References==
{{reflist|25em|refs=

<ref name=AppleInc-c2017-fonts>
{{cite web
 | title=Fonts
 | website=Apple Developer (developer.apple.com)
 | publisher=Apple Inc.
 | url=https://developer.apple.com/fonts/
 | access-date=2017-05-14 | url-status=live
 | archive-url=https://web.archive.org/web/20170508162049/https://developer.apple.com/fonts/
 | archive-date=8 May 2017
}}
</ref>

<!--<ref name=Beeton-Freytag-etal-2015-10-30-slash-0>
{{cite web
 |last1=Beeton  |first1=Barbara 
 |last2=Freytag |first2=Asmus 
 |last3=Iancu   |first3=Laurențiu 
 |last4=Sargent |first4=Murray, III
 |title=Proposal to Represent the Slashed Zero Variant of Empty Set
 |url=https://www.unicode.org/L2/L2015/15268-slashed-zero.pdf
 |website=The Unicode Consortium
 |page=6
 |date=30 October 2015
 |url-status=live
 |archive-url=https://web.archive.org/web/20161021032542/http://www.unicode.org/L2/L2015/15268-slashed-zero.pdf
 |archive-date=21 October 2016
}}
</ref>-->

<ref name=Bemer-1967-08-ACM>
{{cite journal
 |date=August 1967
 |title=Towards standards for handwritten zero and oh: Much ado about nothing (and a letter), or a partial dossier on distinguishing between handwritten zero and oh
 |journal=Communications of the ACM
 |volume=10 |issue=8 |pages=513–518
 |doi=10.1145/363534.363563|s2cid=294510
}}
</ref>

<ref name=Dartmouth-1964-10-01-BASIC>
An "archaic" software document from October&nbsp;1964 showing many examples of the then-prevalent slashed-zero notation in the coding examples.
{{cite web
 |title=BASIC {{grey|[computer programming language]}}
 |date=1 October 1964
 |website=bitsavers.org
 |department=Computation Center
 |publisher=[[Organization:Dartmouth College|Dartmouth College]]
 |url=http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/dartmouth/BASIC_Oct64.pdf
 |url-status=live  |access-date=2021-08-17
 |archive-url=https://web.archive.org/web/20160118030822/http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/dartmouth/BASIC_Oct64.pdf
 |archive-date=18 January 2016
}}
</ref>

<ref name=Greenfield-2013-04-13-piano>
{{cite web
 |author=Adam Greenfield
 |title=That gentle piano is the peace of the grave
 |id=post&nbsp;476182 
 |date=13 April 2013
 |url=http://www.metafilter.com/25220/That-gentle-piano-is-the-peace-of-the-grave#476182
 |archive-url=https://web.archive.org/web/20130413043945/http://www.metafilter.com/25220/That-gentle-piano-is-the-peace-of-the-grave
 |archive-date=2013-04-13
}}
</ref>

<ref name=Nowell-67681-DsgnrNws>
{{cite news
 | last = Nowell | first = Peter
 | title = Apple Reveals San Francisco Monospaced Font
 | id = story&nbsp;67681
 | website = Designer News (designernews.co)
 | url = https://www.designernews.co/stories/67681-apple-reveals-san-francisco-monospaced-font
 | access-date = 2017-05-14 | url-status = live
 | archive-url = https://web.archive.org/web/20161019003838/https://www.designernews.co/stories/67681-apple-reveals-san-francisco-monospaced-font
 | archive-date = 19 October 2016
}}
</ref>

<ref name=Teletype-1948-04-Bul-1164B>
{{cite periodical
 |title=Teletype Printing Telegraph Systems, Keytops, and Typepallets
 |department=Bulletin&nbsp;1164&#x202f;B
 |date=April 1958
 |pages=1–6
 |quote=Teletype part number&nbsp;99564 (keytop).
}}
</ref>

<ref name=Teletype-Bul-1184B>
{{cite periodical
 |title=Teletype Parts Bulletin
 |department=Bulletin&nbsp;1184&#x202f;B
 |pages=27–29
 |id=figure&nbsp;29-31
}}
</ref>

}}

==Sources==
*{{citation |first= Florian |last= Cajori |title= A History of Mathematical Notations |location= Chicago, IL |publisher= Open Court Pub. |year= 1928}}; {{citation |title= op. cit. |location= New York |publisher= Dover Publications |year= 1993 |isbn= 0-486-67766-4 |url-access= registration |url= https://archive.org/details/historyofmathema00cajo_0 }}.

==External links==
*{{citation |chapter-url= http://www.catb.org/~esr/jargon/html/0/numeral-zero.html |chapter= 0 |title= The Jargon File |publisher= Eric S Raymond}}.
*[https://2.bp.blogspot.com/_VfTYpLOGZ3w/Sx7Qq2NSF1I/AAAAAAAAEpo/0wyq40rXrzY/s1600-h/1.jpg Underground Zerø Album Cover] Underground Zerø Band Logo

[[Category:Typographical symbols]]
[[Category:Numeral systems]]
[[Category:0 (number)]]

{{Sourceattribution|Slashed zero}}