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Non-standard units

Humans have always been able to measure things even before the systemisation of measurement by comparing one item to another. This is still widely practiced today, although the comparisons obviously change. Some of these

, sometimes found in books etc., include:

• A ton of
  joules
  .
• The
  books
  as a unit of energy. (Its yield was roughly 13 kilotons.)
• The weight of an elephant. It is often used as a unit of weight in popular books about very big animals such as dinosaurs. This unit needs to be defined, as the real weight of elephants varies much with age and sex and species.

Systems of measurement in the ancient world

Prior to the global adoption of the metric system many different systems of measurement had been in use. Many of these were related to some extent or other. Often they were based on the dimensions of the human body and were effectively a standardisation of previously used measures.

In the History of measurement many of the units that we have records of, or at least the ones that have been used in Europe and around the Mediterranean are variations on older systems originating in the Ancient Near East and Egypt.

Ancient systems of measurement

• Mesopotamian
• Egyptian
  Based on Mesopotamian, developed around 3000BC. Cubit was intl standard
• Persian
  based on mesopotamian, first persian empire c650BC
• Greek
  Derived from egyptian and Mesopotamian and Persian
• Roman
  Based on Greek, also egyptian influences
• Hebrew
  very similar to babylonian system. whatever that is.

Mediæval measurements

Medieval measures can be categorized by ever expanding commercial, political and religious spheres of influence.

Eastern European

In Eastern Europe traditional standards of measure were predominantly of Greek origin

• Polish system
• Romanian system
• Russian system
• Tatar system

Western and Northern European

In Western and Northern Europe traditional standards of measure were predominantly of Roman origin

• Spanish system
• French system
• English system
• Scottish system
• Finnish system
• Danish system
• Norwegian system
• Swedish system
• German system
• Dutch system

Unrelated Historical systems of measurement

• The
  Arabic
  system developed from the Persian system.
• Indus Valley
  developed c2600BC
• Vedic
  Used in Vedic civilisation (began around 1000BC), still used today in Hinduism and Jainism
• Chinese
  Used since 13thC BC, still used today, though adapted to fit metric system.
• Japanese
  Developed from the Chinese System, officially adopted 701BC

Imperial and US customary units

Both the

.

These two systems are closely related. Units of length and area (the inch, foot, yard, mile, acre, etc.) are identical except for surveying purposes. Units of mass and weight differ for units larger than a pound (lb). The Imperial system uses a stone of 14 lb., a long hundredweight of 112 lb. and a long ton of 2240 lb. The stone is not used in the US and the hundredweights and tons are short being 100 lb. and 2000 lb. respectively.

Where these systems most notably differ is in their respective units of volume. A US

, etc. Six US gallons are a little less than five Imperial gallons.

The metric system

Metric systems of units have evolved since the adoption of the first well-defined system in France in 1791. During this evolution the use of these systems spread throughout the world, first to the non-English-speaking countries, and more recently to the English speaking countries.

Multiples and submultiples of metric units are related by powers of ten; the names for these are formed with

. This relationship is compatible with the decimal system of numbers and it contributes greatly to the convenience of metric units.

In the early metric system there were two fundamental or base units, the metre and the kilogram, for length and mass. The other units of length and mass, and all units of area, volume, and compound units such as density were derived from these two fundamental units.

Mesures usuelles (French for customary measurements) were a system of measurement introduced to act as compromise between the metric system and traditional measurements. It was used in France from 1812 to 1939. Similar proposals to metrify the English system of measurement have been put forth but never officially adopted.

A number of variations on the metric system have been in use. These include

of units (mks) most commonly used today.

The current international standard metric system is the

.

The

SI

includes two classes of units which are defined and agreed internationally. The first of these classes are the seven SI base units for length, mass, time, temperature, electric current, luminous intensity and amount of substance. The second of these are the SI derived units. These derived units are defined in terms of the seven base units. All other quantities (e.g. work, force, power) are expressed in terms of SI derived units.

Natural units

The above systems of units are based on arbitrary unit values, formalised as standards. Some unit values occur naturally in Science. Systems of units based on these are called Natural units. The following are examples of these system of natural units.

• Planck units
• Geometrized units

Atomic units

Atomic units (au) are a convenient system of units of measurement used in atomic physics, particularly for describing the properties of electrons. The atomic units have been chosen such that the fundamental electron properties are all equal to one atomic unit.

Currency

For main article see currency

A unit of measurement that applies to

).

See also

• Megalithic yard
• Comparative metrology
• Weights and measures
• Imperial unit
• U.S. customary unit
• SI
• Mesures usuelles
• Metrified English unit
• Units of measurement

External links

• Dictionary of Units of Measurement
• Units of measure
• Unit systems
• Mile measurements
• Old units of measure
• Measures from Antiquity and the Bible