Dab solver - Arbitrary unit

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[[File:IvsV mosfet.svg|thumb|400px|In the vertical axis of this graph, arbitrary unit is used to express approximate trend in the [[current–voltage characteristic]] of a generic [[field-effect transistor]]. It allows to downplay the [[electric current|current]]'s dependence on an individual device (the current depends on its  and other factors). Contrary, the [[voltage]] scale relies on [[...|electronic properties]] of the [[semiconductor]], hence [[volt]]s are given.]]
In [[science]] and [[technology]], an arbitrary unit (abbreviated arb. unit,^ref [[...|see below]])

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[[File:IvsV mosfet.svg|thumb|400px|In the vertical axis of this graph, arbitrary unit is used to express approximate trend in the [[current–voltage characteristic]] of a generic [[field-effect transistor]]. It allows to downplay the [[electric current|current]]'s dependence on an ''individual'' device (the current depends on its <<link:0>> and other factors). Contrary, the [[voltage]] scale relies on [[electronic band structure|electronic properties]] of the [[semiconductor]], hence [[volt]]s are given.]]
In [[science]] and [[technology]], an '''arbitrary unit''' (abbreviated '''arb. unit''',<ref name="iupac1995">{{cite journal |last1=Olesen |first1=H. |last2= |first2= |year=1995 |title=Properties and Units in the Clinical Laboratory Sciences: I. Syntax and Semantic Rules (IUPAC-IFCC Recommendations 1995) |journal=Pure & Appl. Chem. |publisher=IUPAC |volume=87 |issue=8/9 |pages=1563–1574 |url=http://media.iupac.org/publications/labinfo/English/Documents/syntax%20and%20semantic.pdf |doi= }}</ref> ''[[#Abbreviations and nomenclature|see below]]'')
or '''procedure defined unit'''<ref name="iupac2008">{{Cite report |title=Confirmed minutes for the meeting in Uppsala 2008-10-23 – 25 |url=http://www.iupac.org/divisions/VII/VII.C.1/C-NPU_Uppsala_081023_25_minutes_confirmed.pdf |author= |last= |first= |coauthors= |year=2008 |publisher=Committee and Subcommittee on Nomenclature, Properties and Units (SC-C-NPU), [[IUPAC]]–[[IFCC]] |accessdate=September 10, 2010 |docket= }}</ref>{{dead link|date=January 2013}} ('''p.d.u.''')
is a relative [[unit of measurement]] to show the ratio of [[amount of substance]], [[intensity (physics)|intensity]], or other [[quantities]], to a predetermined [[reference]] measurement. The reference measurement is typically defined by the local laboratories or dependent on individual measurement apparatus. It is therefore impossible to compare "1 arb. unit" by one measurer and "1000 arb. unit" by another measurer without detailed prior knowledge on how the respective "arbitrary units" were defined; thus, the unit is sometimes called an '''unknown unit'''.<ref name="iupac2008"/>{{dead link|date=January 2013}} The unit only serves to compare multiple measurements performed in similar environment, since the ratio between the measurement and the reference is a [[dimensionless quantity]] even if value of the reference is unknown in conventional units.
Units of such kind are commonly used in fields such as physiology to indicate [[substance concentration]], and [[spectroscopy]] to express spectral intensity.

When the reference measurement is precisely defined and internationally agreed upon, arbitrary units can also be a unit capable of public comparison. One example of a publicly defined arbitrary unit is the [[International unit|WHO International Unit]].<ref name="iupac2008"/>{{dead link|date=January 2013}}

== Abbreviations and nomenclature ==
Abbreviations for "arbitrary unit" include: '''arb. unit''',<ref name="iupac1995"/> '''arb. u.''', '''AU''',<ref name="jci">{{cite web |url=http://www.jci.org/kiosk/publish/abbreviations |title=Standard abbreviations |date=January 2, 2008 |work=Journal of Clinical Investigation |publisher=American Society for Clinical Investigation |accessdate=September 10, 2010| archiveurl= http://web.archive.org/web/20100728115108/http://www.jci.org/kiosk/publish/abbreviations| archivedate= 28 July 2010 | deadurl= no}}</ref> and '''a.u.'''<ref name="physoc">{{cite web |url=http://ep.physoc.org/site/misc/abbreviationslist.pdf |title=Abbreviations and Symbols List |work=Information and Guidance for Authors, Experimental Physiology |publisher=The Physiological Society |accessdate=September 10, 2010}}</ref>
Among these, "AU" and "a.u." are common abbreviations for [[astronomical unit]]s and [[atomic units]].<ref>{{cite book |title=AIP Style Manual |url=http://www.aip.org/pubservs/style/4thed/toc.html |accessdate=September 9, 2010 |edition=4th |year=1990 |publisher=American Institute of Physics |chapter=Appendix C: Units of Measure |chapterurl=http://www.aip.org/pubservs/style/4thed/appc.pdf| archiveurl= http://web.archive.org/web/20100915110256/http://www.aip.org/pubservs/style/4thed/toc.html| archivedate= 15 September 2010 | deadurl= no}}</ref> For this reason, [[Japanese Journal of Applied Physics]], and probably other [[academic journal]]s, recommend against using "a.u." (Jpn. J. Appl. Phys recommends "arb. unit" instead).<ref>{{cite web|title=Instructions for preparation of manuscript|url=http://jjap.ipap.jp/pdf/instruction_e.pdf|work=Japanese Journal of Applied Physics|publisher=The Japan Society of Applied Physics|accessdate=September 11, 2010}}</ref>

While arbitrary unit is not a formally recognized unit,<ref name=iupac1995 /> [[IUPAC]] and [[IFCC]] recognize the need to deal with "unknown units", and decided in 2008 to use the term "procedure defined unit" in their database.<ref name="iupac2008"/>{{dead link|date=January 2013}} The decision forbids using factors or denominators in conjunction with p.d.u. (such as "p.d.u./L").

== References ==
{{reflist}}

== External links ==
* [http://wiki.answers.com/Q/What_is_Arbitrary_unit What is Arbitrary unit?], [[WikiAnswers]]

{{DEFAULTSORT:Arbitrary Unit}}
[[Category:Units of measurement]]

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Dab solver - Arbitrary unit

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