Cubit

:For the unit of information, see qubit. For the bone, see ulna.

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Cubit is the name for any one of many units of measure used by various ancient peoples, based on the distance between the tip of the middle finger and the elbow on an average person or a similar forearm-based measurement. This definition was often made more specific when a cubit-using culture adopted more standardized measurements. Some cubits are still used today, especially for religious purposes (such as in Judaism).

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The cubit is among the first recorded units of length used by an ancient people. From around 1950 BC, the copper bar cubit of Nippur defines the Sumerian cubit as 517.2 mm (20.36 inches) and is the earliest known length standard.

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While no standard rule exists from Old Kingdom Egypt, it has been securely estabished from surviving architectural evidence that a standard measure was employed as early as c. 2750 BC at Saqqara. From the evidence this is widely accepted to have been 523.5 to 524 mm (20.61 to 20.63 in) in length, and was subdivided into 7 palms of 4 digits, giving a 28 part measure in total. A shorter rule of 6 palms may also have been employed, but based on the same 7 part standard. The basic length was probably originally based on the length of the forearm from the elbow to the middle finger tip. Standard Egyptian cubits survive from later dynasties.

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Many other cultures used cubits as well. Persian cubits were 52–64 cm (20–25 in), the Greek ????? (pechua) was some 47.4 cm (18.7 in), the Roman cubitus was 44.46 cm (17.50 in), the Arabic arsh 48–64 cm (19–28 in), and the אַמָּה (ama) used for Jewish religious purposes today is considered to be some 46–61 cm (18–24 in). The cubit of King Gudea of Lagash (an ancient Mesopotamian city-state) was 495 mm (19? inches). In Izapa, a Precolumbian Mesoamerican city, the measuring unit was also equivalent to 495 mm. This may be coincidence or an indication of diffusion of culture from Mesopotamia to Mesoamerica. In ancient Israel during the First Temple period, the cubit was 428 mm. During the Second Temple period, a cubit of 445 mm was in general use, but in the sacred areas of the temple a special cubit of 437 mm was used instead. (See Biblical Archaeology Review, March-April 1983, and Newsletter and Proceedings of the Society for Early Historical Archaeology, issue 159.)

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Qubit: :A qubit is not to be confused with a cubit, which is an ancient measure of length....

Ulna: The ulna (along with the radius) is one of the two bones in the forearm. In the anatomical position, it is medial to the radius....

Length: In general English usage, length (symbols: l, L) is but one particular instance of distance – an object's length is how long the object is – but in the physical sciences and engineering, the word length is in some contexts used synonymously with "distance". Height is vertical distance; ...