The digit or finger is an ancient and obsolete non- SI

unit of measurement A unit of measurement, or unit of measure, is a definite magnitude (mathematics), magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. Any other qua ...

length Length is a measure of distance. In the International System of Quantities, length is a quantity with Dimension (physical quantity), dimension distance. In most systems of measurement a Base unit (measurement), base unit for length is chosen, ...

. It was originally based on the breadth of a human finger. It was a fundamental unit of length in the

Ancient Egyptian Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...

Mesopotamian Mesopotamia is a historical region of West Asia situated within the Tigris–Euphrates river system, in the northern part of the Fertile Crescent. Today, Mesopotamia is known as present-day Iraq and forms the eastern geographic boundary o ...

Hebrew Hebrew (; ''ʿÎbrit'') is a Northwest Semitic languages, Northwest Semitic language within the Afroasiatic languages, Afroasiatic language family. A regional dialect of the Canaanite languages, it was natively spoken by the Israelites and ...

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), 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 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 The cubit is an ancient unit of length based on the distance from the elbow to the tip of the middle finger. It was primarily associated with the Sumerians, Egyptians, and Israelites. The term ''cubit'' is found in the Bible regarding Noah ...

. On surviving

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.

Mesopotamia

In the classical

Akkadian Empire The Akkadian Empire () was the first known empire, succeeding the long-lived city-states of Sumer. Centered on the city of Akkad (city), Akkad ( or ) and its surrounding region, the empire united Akkadian language, Akkadian and Sumerian languag ...

system instituted in about 2250 BC during the reign of Naram-Sin, the finger was one-thirtieth of a cubit length. The cubit was equivalent to approximately 497 mm, so the finger was equal to about 17 mm. Basic length was used in architecture and field division.

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 The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...

or 3/4" ( 1.905 cm for the international

inch The inch (symbol: in or prime (symbol), ) is a Units of measurement, unit of length in the imperial units, British Imperial and the United States customary units, United States customary System of measurement, systems of measurement. It is eq ...

). 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 A finger is a prominent digit (anatomy), digit on the forelimbs of most tetrapod vertebrate animals, especially those with prehensile extremities (i.e. hands) such as humans and other primates. Most tetrapods have five digits (dactyly, pentadact ...

(7/6 digit),

palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand * Palm plants, of family Arecaceae ** List of Arecaceae genera **Palm oil * Several other plants known as "palm" Palm or Palms may also refer to: Music ...

(4 digits),

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the Koala#Characteristics, koala (which has two thumb#O ...

(16/3 digits), shaftment (8 digits), span (12 digits),

(24 digits) and ell (60 digits).

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 Plutarch (; , ''Ploútarchos'', ; – 120s) was a Greek Middle Platonist philosopher, historian, biographer, essayist, and priest at the Temple of Apollo (Delphi), Temple of Apollo in Delphi. He is known primarily for his ''Parallel Lives'', ...

, XII:23, but the definition as exactly one twelfth of the diameter may be due to

Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...

. 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. The unit was used in Arab or Islamic astronomical works such as those of Ṣadr al‐Sharīʿa al‐Thānī (d.1346/7), where it is called ''iṣba' '', digit or finger. 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. The unit is apparently not in current use, but is found in recent dictionaries.

References

{{DEFAULTSORT:Digit (Length) Units of length Human-based units of measurement