Hand (unit) radix numbering system, where a hand is four inches. The hand, sometimes also called a handbreadth or handsbreadth, is an anthropic unit, originally based on the breadth of a male human hand, either with or without the thumb, or on the height of a clenched fist. On surviving Ancient Egyptian cubit-rods, the royal cubit is divided into seven palms of four digits or fingers each. Five digits are equal to a hand, with thumb; and six to a closed fist. The royal cubit measured approximately 525 mm, so the length of the ancient Egyptian hand was about 94 mm. In
Rack unit Rack unit A rack unit (abbreviated U or RU) is a unit of measure defined as . It is most frequently used as a measurement of the overall height of 19-inch and 23-inch rack frames, as well as the height of equipment that mounts in these frames, whereby the height of the frame or equipment is expressed as multiples of rack units. For example, a typical full-size rack cage is 42U high, while equipment is typically 1U, 2U, 3U, or 4U high. The rack unit size is based on a standard rack specification as defined in EIA-310. The Eurocard specifies