System of units of measurementA system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Instances in use include the International System of Units or () (the modern form of the metric system), the British imperial system, and the United States customary system.
Area densityThe area density (also known as areal density, surface density, superficial density, areic density, mass thickness, column density, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is the kilogram per square metre (kg·m−2). A related area number density can be defined by replacing mass in by number of particles or other countable quantity. In the paper and fabric industries, it is called grammage and is expressed in grams per square meter (g/m2); for paper in particular, it may be expressed as pounds per ream of standard sizes ("basis ream").
Ancient Roman units of measurementThe ancient Roman units of measurement were primarily founded on the Hellenic system, which in turn was influenced by the Egyptian and the Mesopotamian systems. The Roman units were comparatively consistent and well documented. The basic unit of Roman linear measurement was the pes or Roman foot (plural: pedes). Investigation of its relation to the English foot goes back at least to 1647, when John Greaves published his Discourse on the Romane foot.
Ancient Mesopotamian units of measurementAncient Mesopotamian units of measurement originated in the loosely organized city-states of Early Dynastic Sumer. Each city, kingdom and trade guild had its own standards until the formation of the Akkadian Empire when Sargon of Akkad issued a common standard. This standard was improved by Naram-Sin, but fell into disuse after the Akkadian Empire dissolved. The standard of Naram-Sin was readopted in the Ur III period by the Nanše Hymn which reduced a plethora of multiple standards to a few agreed upon common groupings.
Korean units of measurementKorean units of measurement, called cheokgwan-beop () or cheokgeun-beop () in Korean, is the traditional system of measurement used by the people of the Korean peninsula. It is largely based on the Chinese system, with influence from Japanese standards imposed following its annexation of the Korean Empire in 1910. Both North and South Korea currently employ the metric system. Since 2007, South Korea has criminalized the use of Korean units in commercial contexts but informal use continues, especially of the pyeong as a measure of residential and commercial floorspace.
