Digit (unit)

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 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). == 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. 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. ==See also==