System of units of measurement

A 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 SI (the modern form of the metric system), the British imperial system, and the United States customary system.

are useful in relativistic physics. In these systems, speed of light and the gravitational constant are among the constants chosen.

Geometrized unit systems

is system of geometrized units in which the reduced Planck constant is included in the list of defining constants. It is based on only properties of free space rather than of any object or particle.

Planck units

is a system of geometrized units in which the Coulomb constant and the elementary charge are included.

Stoney units

are a system of units used in atomic physics, particularly for describing the properties of electrons. The atomic units have been chosen to use several constants relating to the electron: the electron mass, the elementary charge, the Coulomb constant and the reduced Planck constant. The unit of energy in this system is the total energy of the electron in the Bohr atom and called the Hartree energy. The unit of length is the Bohr radius.

Atomic units

Natural units are units of measurement defined in terms of universal physical constants in such a manner that selected physical constants take on the numerical value of one when expressed in terms of those units. Natural units are so named because their definition relies on only properties of nature and not on any human construct. Varying systems of natural units are possible, depending on the choice of constants used.

Some examples are as follows:

The , which has a playing area 100 yards (91.4 m) long by 160 feet (48.8 m) wide. This is often used by the American public media for the sizes of large buildings or parks. It is used both as a unit of length (100 yd or 91.4 m, the length of the playing field excluding goal areas) and as a unit of area (57,600 sq ft or 5,350 m²), about 1.32 acres (0.53 ha).

American football field

British media also frequently uses the for equivalent purposes, although soccer pitches are not of a fixed size, but instead can vary within defined limits (100–130 yd or 91.4–118.9 m long, and 50–100 yd or 45.7–91.4 m wide, giving an area of 5,000 to 13,000 sq yd or 4,181 to 10,870 m²). However the UEFA Champions League field must be exactly 105 by 68 m (114.83 by 74.37 yd) giving an area of 7,140 m² (0.714 ha) or 8,539 sq yd (1.764 acres). For example, "HSS vessels are aluminium catamarans about the size of a football pitch."^[4]

football pitch

Larger areas are also expressed as a multiple of the areas of certain American states, or subdivisions of the UK etc.

Units of currency[edit]

A unit of measurement that applies to money is called a unit of account in economics and unit of measure in accounting.^[5] This is normally a currency issued by a country or a fraction thereof; for instance, the US dollar and US cent (1⁄100 of a dollar), or the euro and euro cent.

ISO 4217 is the international standard describing three letter codes (also known as the currency code) to define the names of currencies established by the International Organization for Standardization (ISO).

Conversion of units

History of the metric system

ISO 31

Level of measurement

Medieval weights and measures

Megalithic yard

Petrograd Standard

Pseudoscientific metrology

Unified Code for Units of Measure

Weights and measures

Tavernor, Robert (2007), Smoot's Ear: The Measure of Humanity, 0-300-12492-9

ISBN

CLDR – Unicode localization of currency, date, time, numbers

A Dictionary of Units of Measurement

Old units of measure

Antiquity and the Bible at the Wayback Machine (archived May 10, 2008)

Measures from Antiquity and the Bible

Reasonover's Land Measures