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Available in 14 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-14" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">14 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/X-enhed" title="X-enhed – Danish" lang="da" hreflang="da" data-title="X-enhed" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/X-Einheit" title="X-Einheit – German" lang="de" hreflang="de" data-title="X-Einheit" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/X-%C3%BChik" title="X-ühik – Estonian" lang="et" hreflang="et" data-title="X-ühik" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Unidad_X" title="Unidad X – Spanish" lang="es" hreflang="es" data-title="Unidad X" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Siegbahn" title="Siegbahn – French" lang="fr" hreflang="fr" data-title="Siegbahn" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/X%EB%8B%A8%EC%9C%84" title="X단위 – Korean" lang="ko" hreflang="ko" data-title="X단위" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%8E%E0%B4%95%E0%B5%8D%E0%B4%B8%E0%B5%8D_%E0%B4%AF%E0%B5%82%E0%B4%A3%E0%B4%BF%E0%B4%B1%E0%B5%8D%E0%B4%B1%E0%B5%8D" title="എക്സ് യൂണിറ്റ് – Malayalam" lang="ml" hreflang="ml" data-title="എക്സ് യൂണിറ്റ്" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/X%E7%B7%9A%E5%8D%98%E4%BD%8D" title="X線単位 – Japanese" lang="ja" hreflang="ja" data-title="X線単位" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/X-eining" title="X-eining – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="X-eining" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/X_(jednostka_d%C5%82ugo%C5%9Bci)" title="X (jednostka długości) – Polish" lang="pl" hreflang="pl" data-title="X (jednostka długości)" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%98%D0%BA%D1%81-%D0%B5%D0%B4%D0%B8%D0%BD%D0%B8%D1%86%D0%B0" title="Икс-единица – Russian" lang="ru" hreflang="ru" data-title="Икс-единица" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/X-enhet" title="X-enhet – Swedish" lang="sv" hreflang="sv" data-title="X-enhet" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/X_birimi" title="X birimi – Turkish" lang="tr" hreflang="tr" data-title="X birimi" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a 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class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox ib-unit"><tbody><tr><th colspan="2" class="infobox-above">X unit</th></tr><tr><th scope="row" class="infobox-label">Unit of</th><td class="infobox-data"><a href="/wiki/Length" title="Length">length</a></td></tr><tr><th scope="row" class="infobox-label">Symbol</th><td class="infobox-data">xu</td></tr><tr><th colspan="2" class="infobox-header">Conversions </th></tr><tr class="nowrap"><td>1 xu <i>in ...</i></td><td><i>... is equal to ...</i></td></tr><tr style="display:none"><th colspan="2"> </th></tr><tr><th scope="row" class="infobox-label"><span class="nowrap">   </span><a href="/wiki/SI_units" class="mw-redirect" title="SI units">SI units</a></th><td class="infobox-data"><span class="nowrap">   </span><span class="nowrap"><span data-sort-value="6987100210000000000♠"></span>1.0021<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−13</sup> <a href="/wiki/Metre" title="Metre">m</a></span></td></tr><tr><th scope="row" class="infobox-label"><span class="nowrap">   </span><a href="/wiki/Natural_units" title="Natural units">Natural units</a></th><td class="infobox-data"><span class="nowrap">   </span><span class="nowrap"><span data-sort-value="7021620070000000000♠"></span>6.2007<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>21</sup></span> <span class="texhtml"><a href="/wiki/Planck_length" class="mw-redirect" title="Planck length"><var>ℓ</var><sub>P</sub></a></span><br />   <span class="nowrap"><span data-sort-value="6997189370000000000♠"></span>1.8937<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−3</sup></span> <a href="/wiki/Bohr_radius" title="Bohr radius"><i>a</i><sub>0</sub></a></td></tr><tr><th scope="row" class="infobox-label"><span class="nowrap">   </span><a href="/wiki/Imperial_units" title="Imperial units">imperial</a>/<a href="/wiki/US_customary_units" class="mw-redirect" title="US customary units">US</a> units</th><td class="infobox-data"><span class="nowrap">   </span><span class="nowrap"><span data-sort-value="6987100210620000000♠"></span>3.9453<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−12</sup> <a href="/wiki/Inch" title="Inch">in</a></span></td></tr></tbody></table><style data-mw-deduplicate="TemplateStyles:r1236303919">@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-has-images-with-white-backgrounds img{background:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-has-images-with-white-backgrounds img{background:white}}</style> <dl><dd><i>For the software testing tools, see <a href="/wiki/XUnit" title="XUnit">xUnit</a>.</i></dd></dl> <p>The <b>x unit</b> (symbol <b>xu</b>) is a <a href="/wiki/Units_of_measurement" class="mw-redirect" title="Units of measurement">unit</a> of length approximately equal to 0.1 pm (10<sup>−13</sup> m).<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> It is used to quote the <a href="/wiki/Wavelength" title="Wavelength">wavelength</a> of <a href="/wiki/X-ray" title="X-ray">X-rays</a> and <a href="/wiki/Gamma_ray" title="Gamma ray">gamma rays</a>. </p><p>Originally defined by the <a href="/wiki/Sweden" title="Sweden">Swedish</a> physicist <a href="/wiki/Manne_Siegbahn" title="Manne Siegbahn">Manne Siegbahn</a> (1886–1978) in 1925, the x unit could not at that time be measured directly; the definition was instead made in terms of the spacing between planes of the <a href="/wiki/Calcite" title="Calcite">calcite</a> crystals used in the measuring apparatus. One x unit was set at <style data-mw-deduplicate="TemplateStyles:r1154941027">.mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="frac"><span class="num">1</span>⁄<span class="den">3029.04</span></span> of the spacing of the <a href="/wiki/Miller_index" title="Miller index">(200) planes</a> of calcite at 18 <a href="/wiki/Celsius" title="Celsius">°C</a>. </p><p>In modern usage, there are two separate x units, which are defined in terms of the wavelengths of the two most commonly used X-ray lines in <a href="/wiki/X-ray_crystallography" title="X-ray crystallography">X-ray crystallography</a>:<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p> <ul><li>the <b>copper x unit</b> (symbol <b>xu(Cu Kα<sub>1</sub>)</b>) is defined so that the wavelength of the <a href="/wiki/K-alpha" class="mw-redirect" title="K-alpha">Kα<sub>1</sub> line</a> of <a href="/wiki/Copper" title="Copper">copper</a> is exactly 1537.400 xu(Cu Kα<sub>1</sub>);</li> <li>the <b>molybdenum x unit</b> (symbol <b>xu(Mo Kα<sub>1</sub>)</b>) is defined so that the wavelength of the Kα<sub>1</sub> line of <a href="/wiki/Molybdenum" title="Molybdenum">molybdenum</a> is exactly 707.831 xu(Mo Kα<sub>1</sub>).</li></ul> <p>The 2006 <a href="/wiki/Committee_on_Data_for_Science_and_Technology" class="mw-redirect" title="Committee on Data for Science and Technology">CODATA</a> recommended values for these units are:<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <dl><dd>1 xu(Cu Kα<sub>1</sub>) = <span class="nowrap"><span data-sort-value="6987100207699000000♠"></span>1.002<span style="margin-left:.25em;">076</span><span style="margin-left:.25em;">99</span>(28)<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−13</sup> m</span>,</dd> <dd>1 xu(Mo Kα<sub>1</sub>) = <span class="nowrap"><span data-sort-value="6987100209955000000♠"></span>1.002<span style="margin-left:.25em;">099</span><span style="margin-left:.25em;">55</span>(53)<span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>−13</sup> m</span>.</dd></dl> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X_unit&action=edit&section=1" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/%C3%85ngstr%C3%B6m" class="mw-redirect" title="Ångström">Ångström</a></li> <li><a href="/wiki/Angstrom#Angstrom_star" title="Angstrom">Ångström star</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X_unit&action=edit&section=2" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" title="International Union of Pure and Applied Chemistry">IUPAC</a>, <i><a href="/wiki/IUPAC_books#Gold_Book" class="mw-redirect" title="IUPAC books">Compendium of Chemical Terminology</a></i>, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "<a rel="nofollow" class="external text" href="https://goldbook.iupac.org/terms/view/X06719.html">x unit</a>". <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1351%2Fgoldbook.X06719">10.1351/goldbook.X06719</a></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMohrTaylor1999" class="citation journal cs1">Mohr, Peter J.; Taylor, Barry N. (1999). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20171001122752/https://www.nist.gov/sites/default/files/documents/pml/div684/fcdc/rmp1998-2.pdf">"CODATA recommended values of the fundamental physical constants: 1998"</a> <span class="cs1-format">(PDF)</span>. <i><a href="/wiki/Journal_of_Physical_and_Chemical_Reference_Data" title="Journal of Physical and Chemical Reference Data">Journal of Physical and Chemical Reference Data</a></i>. <b>28</b> (6): 1713–1852. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1999JPCRD..28.1713M">1999JPCRD..28.1713M</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1063%2F1.556049">10.1063/1.556049</a>. Archived from <a rel="nofollow" class="external text" href="https://www.nist.gov/pml/div684/fcdc/upload/rmp1998-2.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2017-10-01.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Journal+of+Physical+and+Chemical+Reference+Data&rft.atitle=CODATA+recommended+values+of+the+fundamental+physical+constants%3A+1998&rft.volume=28&rft.issue=6&rft.pages=1713-1852&rft.date=1999&rft_id=info%3Adoi%2F10.1063%2F1.556049&rft_id=info%3Abibcode%2F1999JPCRD..28.1713M&rft.aulast=Mohr&rft.aufirst=Peter+J.&rft.au=Taylor%2C+Barry+N.&rft_id=https%3A%2F%2Fwww.nist.gov%2Fpml%2Fdiv684%2Ffcdc%2Fupload%2Frmp1998-2.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX+unit" class="Z3988"></span></span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMohrTaylorNewell2008" class="citation journal cs1">Mohr, Peter J.; Taylor, Barry N.; Newell, David B. (2008). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20171001121533/https://www.nist.gov/sites/default/files/documents/pml/div684/fcdc/rmp2006-2.pdf">"CODATA Recommended Values of the Fundamental Physical Constants: 2006"</a> <span class="cs1-format">(PDF)</span>. <i><a href="/wiki/Reviews_of_Modern_Physics" title="Reviews of Modern Physics">Reviews of Modern Physics</a></i>. <b>80</b> (2): 633–730. <a href="/wiki/ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://arxiv.org/abs/0801.0028">0801.0028</a></span>. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2008RvMP...80..633M">2008RvMP...80..633M</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1103%2FRevModPhys.80.633">10.1103/RevModPhys.80.633</a>. Archived from <a rel="nofollow" class="external text" href="https://www.nist.gov/pml/div684/fcdc/upload/rmp2006-2.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2017-10-01.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Reviews+of+Modern+Physics&rft.atitle=CODATA+Recommended+Values+of+the+Fundamental+Physical+Constants%3A+2006&rft.volume=80&rft.issue=2&rft.pages=633-730&rft.date=2008&rft_id=info%3Aarxiv%2F0801.0028&rft_id=info%3Adoi%2F10.1103%2FRevModPhys.80.633&rft_id=info%3Abibcode%2F2008RvMP...80..633M&rft.aulast=Mohr&rft.aufirst=Peter+J.&rft.au=Taylor%2C+Barry+N.&rft.au=Newell%2C+David+B.&rft_id=https%3A%2F%2Fwww.nist.gov%2Fpml%2Fdiv684%2Ffcdc%2Fupload%2Frmp2006-2.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX+unit" class="Z3988"></span></span> </li> </ol></div></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=X_unit&oldid=1225194701">https://en.wikipedia.org/w/index.php?title=X_unit&oldid=1225194701</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Help:Category" title="Help:Category">Categories</a>: <ul><li><a href="/wiki/Category:Units_of_length" title="Category:Units of length">Units of length</a></li><li><a href="/wiki/Category:Customary_units_of_measurement" title="Category:Customary units of measurement">Customary units of measurement</a></li><li><a href="/wiki/Category:X-rays" title="Category:X-rays">X-rays</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 22 May 2024, at 22:53<span class="anonymous-show"> (UTC)</span>.</li> <li id="footer-info-copyright">Text is available under the <a href="/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License" title="Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License">Creative Commons Attribution-ShareAlike 4.0 License</a>; additional terms may apply. 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