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The digit or finger is an ancient and obsolete non-SI unit of measurement of length. It is an anthropic unit, originally based on the breadth of a human finger. It was a fundamental unit of length in the Ancient Egyptian, Mesopotamian, Hebrew, Ancient Greek and Roman systems of measurement.

In astronomy a digit is one twelfth of the diameter of the sun or the moon.

History

Ancient Egypt

The digit, also called a finger or fingerbreadth, is an anthropic unit originally based on the breadth of a human finger. In Ancient Egypt it was the basic unit of subdivision of the cubit.

On surviving Ancient Egyptian cubit-rods, the royal cubit is divided into seven palms of four digits or fingers each. The royal cubit measured approximately 525 mm, so the length of the ancient Egyptian digit was about 19 mm.

Ancient Egyptian units of length

Name	Egyptian name	Equivalent Egyptian values	Metric equivalent
Royal cubit	meh niswt	7 palms or 28 digits	525 mm
Fist		6 digits	108 mm
Hand		5 digits	94 mm
Palm	shesep	4 digits	75 mm
Digit	djeba	1/4 palm	19 mm

Mesopotamia

Ancient Hebrew system

Ancient Greece

Ancient Rome

Britain

A digit (lat. digitus, "finger"), when used as a unit of length, is usually a sixteenth of a foot or 3/4" (1.905 cm for the international inch). 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 (7/6 digit), palm (4 digits), hand (16/3 digits), shaftment (8 digits), span (12 digits), cubit (24 digits) and ell (60 digits).

It is in general equal to the foot-nail, although the term nail can also be used as 1/16 of yard and other units.

Astronomy

In astronomy a digit is, or was until recently, one twelfth of the diameter of the sun or the moon. This is found in the Moralia of Plutarch, XII:23, 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.

See also

• Cubit

References

1. ^ Hosch, William L. (ed.) (2010) The Britannica Guide to Numbers and Measurement New York, NY: Britannica Educational Publications, 1st edition. ISBN978-1615301089, p.203}}
2. ^ Chisholm, Hugh (ed.) (1910–1911) Encyclopædia Britannica (11th edition) Cambridge: University Press, "digit"
3. Selin, Helaine (ed.) (1997). Encyclopaedia of the History of Science, Technology and Medicine in non-Western Cultures. Dordrecht: Kluwer. ISBN 9780792340669. {{cite book}}: |first= has generic name (help)
4. Lepsius, Richard (1865). Die altaegyptische Elle und ihre Eintheilung (in German). Berlin: Dümmler.
5. Clagett, Marshall (1999). Ancient Egyptian Science, A Source Book. Volume 3: Ancient Egyptian Mathematics. Philadelphia: American Philosophical Society. ISBN 9780871692320.
6. {Macdonald, A.M. (ed.) (1972) Chambers Twentieth Century Dictionary Edinburgh: W. & R. Chambers, "digit"
7. Plutarchus Chaeronensis, Frank Cole Babbitt (trans.) (1957) Plutarch's Moralia: In fifteen volumes London: William Heinemann, Cambridge, Mass.: Harvard University Press, Volume XII p.144
8. Neugebauer, Otto (1975) A History of Ancient Mathematical Astronomy Berlin: Springer, Volume 2, p.658

• Units of length
• Human-based units of measure