Editing Digit (unit)

{{Other uses|Digit (disambiguation){{!}}Digit}}
[[File:Coudée-turin detail.jpg|thumb|right|250px|Detail of the Ancient Egyptian cubit rod in the [[Museo Egizio]] of [[Turin]], showing digit, palm, hand and fist lengths]]
[[File:Hand Units of Measurement.PNG|thumb|Some hand-based measurements, including the digit (6)]]
The '''digit''' or '''finger''' is an ancient and obsolete non-[[SI]] [[Units of measure|unit of measurement]] of [[length]]. It was originally based on the breadth of a human finger.<ref name=brit/> It was a fundamental unit of length in the [[Ancient Egyptian units of measurement|Ancient Egyptian]], [[Ancient Mesopotamian units of measurement|Mesopotamian]], [[Ancient Hebrew units of measurement|Hebrew]], [[Ancient Greek units of measurement|Ancient Greek]] and [[Ancient Roman units of measurement|Roman]] systems of measurement.

In astronomy a digit is one twelfth of the diameter of the sun or the moon.<ref name=11th/>

==History==
===Ancient Egypt===
{{main|Ancient Egyptian units of measurement}}
The digit, also called a finger or fingerbreadth, is a unit of measurement originally based on the breadth of a human finger. In Ancient Egypt it was the basic unit of subdivision of the [[cubit]].<ref name=brit/>

On surviving [[Ancient Egyptian units of measurement|Ancient Egyptian]] [[Measuring rod#Ancient Egypt|cubit-rods]], the [[Cubit#Ancient Egyptian royal cubit|royal cubit]] is divided into seven [[Palm (length)|palms]] of four digits or fingers each.<ref name=selin/> The royal cubit measured approximately 525&nbsp;mm,<ref name=lepsius/> so the length of the ancient Egyptian digit was about 19&nbsp;mm.
{| class="wikitable"| style="margin: 1em auto 1em auto; width: 75%; nowrap"
|+'''Ancient Egyptian units of length'''<ref name=clagett/>
!|Name!! |Egyptian name!!align="center"|Equivalent Egyptian values!! |Metric equivalent
|-
|Royal cubit ||  <small><hiero>M23-t:n-D42</hiero> </small> ''meh niswt'' || align="center" | 7 palms or 28 digits || align="right" | 525&nbsp;mm&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
|-
|Fist ||  <!---<small><hiero>?</hiero> </small> '' ??? ''---> ||align="center" | 6 digits ||align="right" | 108&nbsp;mm&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
|-
|Hand ||  <!---<small><hiero>?</hiero> </small> '' ??? ''---> ||align="center" | 5 digits ||align="right" | 94&nbsp;mm&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
|-
|Palm ||  <small><hiero>D48</hiero> </small> ''shesep'' || align="center" | 4 digits||align="right" | 75&nbsp;mm&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
|-
|Digit ||  <small><hiero> D50</hiero> </small> ''djeba'' || align="center" | 1/4 palm ||align="right" | 19&nbsp;mm&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
|}

=== Mesopotamia ===
{{main|Ancient Mesopotamian units of measurement}}

In the classical [[Akkadian Empire]] system instituted in about 2250 BC during the reign of [[Naram-Sin of Akkad|Naram-Sin]], the finger was one-thirtieth of a cubit length. The cubit was equivalent to approximately 497&nbsp;mm, so the finger was equal to about 17&nbsp;mm. Basic length was used in architecture and field division.   
{| class="wikitable"| style="margin: 1em auto 1em auto;  nowrap"
|+ Mesopotamian units of length
|-
!Unit ||Ratio ||&nbsp;Metric<br>equivalent&nbsp; ||&nbsp;Sumerian&nbsp; ||&nbsp;Akkadian&nbsp; ||&nbsp;Cuneiform&nbsp; 
|-
| &nbsp;grain ||align="center" |&nbsp;&nbsp;1/180&nbsp;&nbsp; ||align="right" | 2.8&nbsp;mm&nbsp;&nbsp;  ||&nbsp;še ||&nbsp;''uţţatu'' ||&nbsp;{{cuneiform|𒊺}}
|-
| &nbsp;finger&nbsp;&nbsp; ||align="center" |1/30 ||align="right" | 17&nbsp;mm&nbsp;&nbsp;||&nbsp;šu-si ||&nbsp;''ubānu''||&nbsp;{{cuneiform|𒋗}}{{cuneiform|𒋛}}
|-
| &nbsp;foot ||align="center" |2/3 ||align="right" | 331&nbsp;mm&nbsp;&nbsp;  ||&nbsp;šu-du<sub>3</sub>-a ||&nbsp;''šīzu'' ||&nbsp;{{cuneiform|𒋗}}{{cuneiform|𒆕}}{{cuneiform|𒀀}}
|-
| &nbsp;[[cubit]] ||align="center" |1 ||align="right" | 497&nbsp;mm&nbsp;&nbsp;  ||&nbsp;kuš<sub>3</sub> ||&nbsp;''ammatu'' ||&nbsp;{{cuneiform|𒌑}}

|}

=== Ancient Hebrew system ===
{{main|Ancient Hebrew units of measurement}}

=== Ancient Greece ===
{{main|Ancient Greek units of measurement}}

=== Ancient Rome ===
{{main|Ancient Roman units of measurement}}

=== Britain ===
{{main|English units}}
A '''digit''' ([[Latin language|lat.]] ''digitus'', "finger"), when used as a unit of length, is usually a sixteenth of a [[foot (unit)|foot]] or 3/4" ([[1 E-2 m|1.905 cm]] for the international [[inch]]).<ref name="Zupko1985">{{cite book|author=Ronald Edward Zupko|authorlink=Ronald Edward Zupko|title=A dictionary of weights and measures for the British Isles: the Middle Ages to the twentieth century|url=https://archive.org/details/bub_gb_0l_k-XMIiQIC|accessdate=15 January 2012|year=1985|publisher=American Philosophical Society|isbn=978-0-87169-168-2|pages=[https://archive.org/details/bub_gb_0l_k-XMIiQIC/page/n143 109]–10}}</ref> The width of an adult human male finger tip is indeed about 2 centimetres. In English this unit has mostly fallen out of use, as do others based on the human arm: [[finger (unit)|finger]] (7/6 digit), [[palm (unit)|palm]] (4 digits), [[hand (unit)|hand]] (16/3 digits), [[shaftment]] (8 digits), [[span (length)|span]] (12 digits), [[cubit]] (24 digits) and [[ell (unit)|ell]] (60 digits).

== Astronomy ==
In astronomy a digit is, or was until recently, one twelfth of the diameter of the sun or the moon.<ref name=11th/><ref name=chamb/> This is found in the [[Moralia]] of [[Plutarch]], XII:23,<ref name=plut/> but the definition as exactly one twelfth of the diameter may be due to [[Ptolemy]]. [[Sosigenes of Alexandria]] had observed in the 1st century AD that on a [[dioptra]], a disc with a diameter of 11 or 12 digits (of length) was needed to cover the moon.<ref name=neug/>

The unit was used in Arab or Islamic astronomical works such as those of [[Ṣadr al‐Sharīʿa al‐Thānī]] (d.1346/7),<ref name=hockey/> where it is called {{langx|ar|إصبعا}} ''iṣba' '', digit or finger.<ref name=sadr/>

The astronomical digit was in use in Britain for centuries. Heath, writing in 1760, explains that 12 digits are equal to the diameter in eclipse of the sun, but that 23 may be needed for the Earth's shadow as it eclipses the moon, those over 12 representing the extent to which the Earth's shadow is larger than the Moon.<ref name=heath/> The unit is apparently not in current use, but is found in recent dictionaries.<ref name=chamb/>

==See also==
* [[Finger (unit)]]
* [[Finger tip unit]]
* [[Cubit]]
* [[Anthropic units]]

== References ==
{{reflist|refs=

<ref name=11th>{{cite EB1911|wstitle=Digit |volume=8 |page=268}}</ref>

<ref name=brit>Hosch, William L. (ed.) (2010) [https://books.google.com/books?id=cuN7rH6RzikC ''The Britannica Guide to Numbers and Measurement''] New York, NY: Britannica Educational Publications, 1st edition. {{ISBN|978-1-61530-108-9}}, p.203</ref>

<ref name=chamb>Macdonald, A.M. (ed.) (1972) ''Chambers Twentieth Century Dictionary'' Edinburgh: W. & R. Chambers {{ISBN|0-550-10206-X}}, "digit"</ref>

<ref name=clagett>{{cite book|last=Clagett|first=Marshall|title=Ancient Egyptian Science, A Source Book. Volume 3: Ancient Egyptian Mathematics|year= 1999|publisher= American Philosophical Society|location= Philadelphia|isbn= 978-0-87169-232-0|url= https://archive.org/details/bub_gb_8c10QYoGa4UC}}</ref>

<ref name=heath>{{cite book |last=Heath |first=Robert |authorlink=Robert Heath (mathematician) |year=1760 |url=https://archive.org/details/astronomiaaccur00heatgoog |title=Astronomia accurata; or ... subservient to the three principal Subjects |publisher=Published by the author. |location= London |page=ix}}</ref>

<ref name=hockey>Hockey, Thomas et al. (eds.) (2007) [http://islamsci.mcgill.ca/RASI/BEA/Sadr_al-Sharia_al-Thani_BEA.htm ''The Biographical Encyclopedia of Astronomers, Springer Reference''] New York: Springer pp. 1002–1003</ref>

<ref name=lepsius>{{cite book|last=Lepsius|first=Richard|title=Die altaegyptische Elle und ihre Eintheilung|year=1865|publisher=Dümmler|location=Berlin|url=https://archive.org/details/bub_gb_PRQGAAAAQAAJ|language=German}}</ref>

<ref name=neug>[[Otto Neugebauer|Neugebauer, Otto]] (1975) [https://books.google.com/books?id=vO5FCVIxz2YC ''A History of Ancient Mathematical Astronomy''] Berlin: Springer, {{ISBN|978-0-387-06995-1}} Volume 2, p.658</ref>

<ref name=plut>Plutarchus Chaeronensis, Frank Cole Babbitt (trans.) (1957) [https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Moralia/The_Face_in_the_Moon*/C.html#ref226 ''Plutarch's Moralia: In fifteen volumes''] London: William Heinemann, Cambridge, Mass.: Harvard University Press, Volume XII p.144</ref>

<ref name=sadr>'Ubayd Allāh ibn Mas'ūd Ṣadr al-S̆arīaẗ al-Aṣġar al-Maḥbūbī, Ahmad S. Dallal (1995) [https://books.google.com/books?id=ULp2LGmKTSMC ''An Islamic response to Greek astronomy: kitāb Ta'dīl hay'at al-aflāk of Ṣadr al-Sharī'a''] (in Arabic and English) Leiden, New York: E.J. Brill, {{ISBN|978-90-04-09968-5}} p.212</ref>

<ref name=selin>{{cite book|editor-last=Selin|editor-first=Helaine|editor-link=Helaine Selin|title=Encyclopaedia of the History of Science, Technology and Medicine in non-Western Cultures|year= 1997|publisher= Kluwer|location= Dordrecht|isbn= 978-0-7923-4066-9|url=https://books.google.com/books?id=raKRY3KQspsC}}</ref>

}}

{{DEFAULTSORT:Digit (Length)}}
[[Category:Units of length]]
[[Category:Human-based units of measurement]]