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Encyclopedia > International System of Units
Cover of brochure The International System of Units.
Cover of brochure The International System of Units.

The International System of Units (abbreviated SI from the French Le Système International d'Unités[1]) is the modern form of the metric system and is generally a system devised around the convenience of the number 10. It is the world's most widely used system of units, both in everyday commerce and in science.[2] An extensive presentation of the SI units is maintained on line by NIST, including a diagram of the interrelations between the derived units based upon the SI units. Definitions of the basic units can be found on this site, as well as the CODATA report listing values for special constants such as the electric constant, the magnetic constant and the speed of light, all of which have defined values as a result of the definition of the metre and ampere.[3] Si or si or SI may stand for: SI, the Système International dUnités (the metric International System of Units) one of two Spanish words pronounced like see: sí (accented) for yes and si (unaccented) for if in music, Si, the seventh note of solfege in chemistry, Si, the chemical... Image File history File links SI_Brochure_Cover. ... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful. ... This article does not cite any references or sources. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... The electric constant () is the permittivity of vacuum, a physical constant, defined by: where: - magnetic constant - speed of light In SI units, the value is exactly expressed by: = 2. ... The magnetic constant () is the permeability of vacuum. ... A line showing the speed of light on a scale model of Earth and the Moon, taking about 1â…“ seconds to traverse that distance. ...


The older metric system included several groups of units. The SI was developed in 1960 from the old metre-kilogram-second (mks) system, rather than the centimetre-gram-second (cgs) system, which, in turn, had a few variants. Because the SI is not static units are created and definitions are modified through international agreement among many nations as the technology of measurement progresses, and as the precision of measurements improves. Year 1960 (MCMLX) was a leap year starting on Friday (link will display full calendar) of the Gregorian calendar. ... This article is about the unit of length. ... Kg redirects here. ... This article is about the unit of time. ... This article or section is in need of attention from an expert on the subject. ...


The system is nearly universally employed, and most countries do not even maintain official definitions of any other units. A notable exception is the United States, which still uses many old units in addition to SI. In the United Kingdom, conversion to metric units is government policy, but the transition is not yet complete. Those countries that still recognise non-SI units (e.g. the US and UK) have redefined their traditional non-SI units in terms of SI units. Metrication or metrification refers to the introduction of the SI metric system as the international standard for physical measurements—a long-term series of independent and systematic conversions from the various separate local systems of weights and measures. ... Conversion of units refers to conversion factors between different units of measurement for the same quantity. ...

Three nations have not officially adopted the International System of Units as their primary or sole system of measurement: Liberia, Myanmar and the United States.
Three nations have not officially adopted the International System of Units as their primary or sole system of measurement: Liberia, Myanmar and the United States.

Contents

Image File history File links Download high-resolution version (1427x628, 47 KB)hey yo jenny. ... Image File history File links Download high-resolution version (1427x628, 47 KB)hey yo jenny. ... Anthem: Kaba Ma Kyei Capital Naypyidaw , Largest city Yangon (Rangoon) Official languages Burmese Recognised regional languages Jingpho, Shan, Karen, Mon, Rakhine Demonym Burmese Government Military junta  -  Chairman of the State Peace and Development Council Senior General Than Shwe  -  Vice Chairman of the State Peace and Development Council Vice-Senior General...

Realisation of units

It is important to distinguish between the definition of a unit and its realization. The definition of each base unit of the SI is carefully drawn up so that it is unique and provides a sound theoretical basis upon which the most accurate and reproducible measurements can be made. The realization of the definition of a unit is the procedure by which the definition may be used to establish the value and associated uncertainty of a quantity of the same kind as the unit. A description of how the definitions of some important units are realized in practice is given on the BIPM website,

SI Practical Realization brochure

A coherent SI derived unit is defined uniquely only in terms of SI base units. For example, the coherent SI derived unit of resistance, the ohm, symbol Ω, is uniquely defined by the relation Ω = m2 kg s−3 A−2, which follows from the definition of the quantity electrical resistance. However any method consistent with the laws of physics could be used to realize any SI unit.[4]


History

The metric system was conceived by a group of scientists (among them, Antoine-Laurent Lavoisier, who is known as the "father of modern chemistry") which had been commissioned by King Louis XVI of France to create a unified and rational system of measures. After the French Revolution, the system was adopted by the new government.[5] On August 1, 1793, the National Convention adopted the new decimal "metre" with a provisional length as well as the other decimal units with preliminary definitions and terms. On April 7, 1795 (Loi du 18 germinal, an III) the terms gramme and kilogramme replaced the former terms "gravet" (correctly "milligrave") and "grave". On December 10, 1799 (a month after Napoleon's coup d'etat), the metric system was definitively adopted in France. This article is about the unit of length. ... now. ... Kg redirects here. ... This article is about the unit of time. ... For other uses, see Ampere (disambiguation). ... For other uses, see Kelvin (disambiguation). ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... The coulomb (symbol: C) is the SI unit of electric charge. ... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... Lavoisier redirects here. ... Louis XVI Louis XVI (August 23, 1754 - January 21, 1793), was King of France and Navarre from 1774 until 1791, and then King of the French in 1791-1792. ... The French Revolution (1789–1815) was a period of political and social upheaval in the political history of France and Europe as a whole, during which the French governmental structure, previously an absolute monarchy with feudal privileges for the aristocracy and Catholic clergy, underwent radical change to forms based on... is the 213th day of the year (214th in leap years) in the Gregorian calendar. ... Year 1793 (MDCCXCIII) was a common year starting on Tuesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Saturday of the 11-day slower Julian calendar). ... April 7 is the 97th day of the year in the Gregorian calendar (98th in leap years). ... 1795 was a common year starting on Thursday (see link for calendar). ... now. ... is the 344th day of the year (345th in leap years) in the Gregorian calendar. ... 1799 was a common year starting on Tuesday (see link for calendar). ... Napoléon Bonaparte in the coup détat of 18 brumaire. ...


The history of the metric system has seen a number of variations, whose use has spread around the world, to replace many traditional measurement systems. At the end of World War II a number of different systems of measurement were still in use throughout the world. Some of these systems were metric-system variations, while others were based on the Imperial and American systems. It was recognized that additional steps were needed to promote a worldwide measurement system. As a result the 9th General Conference on Weights and Measures (CGPM), in 1948, asked the International Committee for Weights and Measures (CIPM) to conduct an international study of the measurement needs of the scientific, technical, and educational communities. The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... A system of measurement is a set of units which can be used to specify anything which can be measured and were historically important, regulated and defined because of trade and internal commerce. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... This article is about post-1824 imperial units, see also English unit, U.S. customary units or Avoirdupois. ... The U.S. customary units (more commonly known in the US as English units or standard units) are the non-metric units of measurement that are presently used in the United States, in some cases alongside the metric system of units. ... Metrication or metrification refers to the introduction of the SI metric system as the international standard for physical measurements—a long-term series of independent and systematic conversions from the various separate local systems of weights and measures. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, never GCWM). ... The International Committee for Weights and Measures is the English name of the Comité international des poids et mesures (CIPM, sometimes written in English Comité International des Poids et Mesures). ...


Based on the findings of this study, the 10th CGPM in 1954 decided that an international system should be derived from six base units to provide for the measurement of temperature and optical radiation in addition to mechanical and electromagnetic quantities. The six base units recommended were the metre, kilogram, second, ampere, degree Kelvin (later renamed the kelvin), and the candela. In 1960, the 11th CGPM named the system the International System of Units, abbreviated SI from the French name: Le Système international d'unités. The seventh base unit, the mole, was added in 1971 by the 14th CGPM. This article is about the unit of length. ... Kg redirects here. ... This article is about the unit of time. ... For other uses, see Ampere (disambiguation). ... For other uses, see Kelvin (disambiguation). ... Photopic (black) and scotopic [1] (green) luminosity functions. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ...


Future development

The ISO standard ISO 31 contains recommendations for the use of the International System of Units; for applications in electrical applications additionally the IEC standard IEC 60027 has to be taken into account. As of 2008, work is proceeding to integrate both standards into a joint standard Quantities and Units in which the quantities and equations used with SI are to be referred as the International System of Quantities (ISQ). “ISO” redirects here. ... International Standard ISO 31 (Quantities and units, International Organization for Standardization, 1992) is the most widely respected style guide for the use of units of measurement, and formulas involving them, in scientific and educational documents worldwide. ... The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ... IEC 60027 (formerly IEC 27) is the International Electrotechnical Commissions standard on Letter symbols to be used in electrical technology. ... International Standard ISO 80000 (Quantities and units, International Organization for Standardization) is the most widely respected style guide for the use of units of measurement, and formulas involving them, in scientific and educational documents worldwide. ...


Units

The international system of units consists of a set of units together with a set of prefixes. The units of SI can be divided into two subsets. There are seven base units. Each of these base units is nominally dimensionally independent. From these seven base units several other units are derived. In addition to the SI units there is also a set of non-SI units accepted for use with SI. The SI system of units defines seven SI base units: physical units defined by an operational definition. ... SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ... An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ... An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ... The following units are not SI units but are accepted for use with the International System. ...

SI base units[6]
Name Symbol Quantity
metre m length
kilogram kg mass
second s time
ampere A electric current
kelvin K thermodynamic temperature
mole mol amount of substance
candela cd luminous intensity

A prefix may be added to a unit to produce a multiple of the original unit. All multiples are integer powers of ten. For example, kilo- denotes a multiple of a thousand and milli- denotes a multiple of a thousandth; hence there are one thousand millimetres to the metre and one thousand metres to the kilometre. The prefixes are never combined: a millionth of a kilogram is a milligram not a microkilogram. This article is about the unit of length. ... For other uses of this word, see Length (disambiguation). ... Kg redirects here. ... For other uses, see Mass (disambiguation). ... This article is about the unit of time. ... This article is about the concept of time. ... For other uses, see Ampere (disambiguation). ... This box:      Electric current is the flow (movement) of electric charge. ... For other uses, see Kelvin (disambiguation). ... Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... The amount of substance, n, of a sample or system is a physical quantity which is proportional to the number of elementary entities present. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... Luminous intensity is a measure of the energy emitted by a light source in a particular direction. ... An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ...

Standard prefixes for the SI units of measure
Multiples Name deca- hecto- kilo- mega- giga- tera- peta- exa- zetta- yotta-
Symbol da h k M G T P E Z Y
Factor 100 101 102 103 106 109 1012 1015 1018 1021 1024
 
Subdivisions Name deci- centi- milli- micro- nano- pico- femto- atto- zepto- yocto-
Symbol d c m µ n p f a z y
Factor 100 10−1 10−2 10−3 10−6 10−9 10−12 10−15 10−18 10−21 10−24

An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ... This article is about the SI prefix. ... Hecto (symbol h) is a SI prefix in the SI system of units denoting a factor of 102 (100). ... Kilo (symbol: k) is a prefix in the SI system denoting 103 or 1,000. ... Mega (symbol M) is a SI prefix in the SI system of units denoting a factor of 106, i. ... Look up giga- in Wiktionary, the free dictionary. ... Tera (symbol: T) is a prefix in the SI system of units denoting 1012, or 1 000 000 000 000. ... This article describes the SI prefix peta. ... Exa (symbol E) is a prefix in the SI system of units denoting 1018 or 1 000 000 000 000 000 000. ... Zetta (symbol Z) is a SI prefix in the SI system of units denoting 1021 or 1 000 000 000 000 000 000 000. ... Yotta (symbol Y) is a SI prefix in the SI system of units denoting 1024 or 1 000 000 000 000 000 000 000 000. ... Deci- is a Latin numerical prefix meaning 10. ... Centi (symbol c) is a SI prefix in the SI system of units denoting a factor of 10-2, or 1/100. ... Milli (symbol m) is a SI prefix in the SI system of units denoting a factor of 10-3, or 1/1,000. ... Micro is a SI prefix in the SI system of units denoting a factor of 10−6 (one millionth). ... This article describes the SI prefix. ... For other meanings of Pico see Pico (disambiguation) Pico (symbol p) is a prefix in the SI system of units denoting a factor of 10-12. ... Femto is a prefix (see all prefixes) to a unit and means that it is 10-15 times this unit, or, one quindecillionth (European) or one quadrillionth (American). ... Atto- (symbol a) is an SI prefix to a unit and means that it is 10-18 times this unit. ... Zepto (symbol z) is a prefix in the SI system of units denoting a factor of 10-21. ... Look up yocto- in Wiktionary, the free dictionary. ...

SI writing style

  • Symbols do not have an appended period/full stop (.) unless at the end of a sentence.
  • Symbols are written in upright (Roman) type (m for metres, l for litres), so as to differentiate from the italic type used for variables (m for mass, l for length). By consensus of international standards bodies, this rule is applied independent of the font used for surrounding text.[7]
  • Symbols for units are written in lower case, except for symbols derived from the name of a person. For example, the unit of pressure is named after Blaise Pascal, so its symbol is written "Pa" whereas the unit itself is written "pascal". All symbols of prefixes larger than 103 (kilo) are also uppercase.
    • The one exception is the litre, whose original symbol "l" is unsuitably similar to the numeral "1" or the uppercase letter "i" (depending on the typeface used), at least in many English-speaking countries. The American National Institute of Standards and Technology recommends that "L" be used instead, a usage which is common in the US, Canada, Australia (but not elsewhere). This has been accepted as an alternative by the CGPM since 1979. The cursive ℓ is occasionally seen, especially in Japan and Greece, but this is not currently recommended by any standards body. For more information, see Litre.
  • The SI rule for pluralising units is that symbols of units are not pluralised, for example "25 kg" (not "25 kgs").[7]
    • The American National Institute of Standards and Technology has defined guidelines for American users of the SI.[8][9]These guidelines give guidance on pluralizing unit names: the plural is formed by using normal English grammar rules, for example, "henries" is the plural of "henry". The units lux, hertz, and siemens are exceptions from this rule: they remain the same in singular and plural. Note that this rule only applies to the full names of units, not to their symbols.
  • A space separates the number and the symbol, e.g. "2.21 kg", "7.3×102 m²", "22 K".[10][11] Exceptions are the symbols for plane angular degrees, minutes and seconds (°, ′ and ″), which are placed immediately after the number with no intervening space.
  • Spaces may be used as a thousands separator (1 000 000) in contrast to commas or periods (1,000,000 or 1.000.000) in order to reduce confusion resulting from the variation between these forms in different countries. In print, the space used for this purpose is typically narrower than that between words (commonly a thin space).
  • Any line break inside a number, inside a compound unit or between number and unit should be avoided, but if necessary the latter option should be used.
  • The 10th resolution of CGPM in 2003 declared that "the symbol for the decimal marker shall be either the point on the line or the comma on the line". In practice, the decimal point is used in English and the comma in most other European languages.
  • Symbols for derived units formed from multiple units by multiplication are joined with a space or centre dot (·), for example "N m" or "N·m".[12]
  • Symbols formed by division of two units are joined with a solidus (⁄), or given as a negative exponent. For example, the "metre per second" can be written "m/s", "m s−1", "m·s−1" or textstylefrac{mathrm{m}}{mathrm{s}}. Only one solidus should be used, i.e. "kg·m−1·s−2" is preferable to "kg/m/s²", and "kg/m·s²" is something else. Many computer users will type the / character provided on computer keyboards, which in turn produces the Unicode character U+002F, which is named solidus but is distinct from the Unicode solidus character, U+2044.
  • In Chinese, Japanese, and Korean language computing (CJK), some of the commonly used units, prefix-unit combinations, or unit-exponent combinations have been allocated predefined single characters taking up a full square. Unicode includes these in its CJK Compatibility and Letterlike Symbols subranges for back compatibility, without necessarily recommending future usage.
  • When writing dimensionless quantities, the terms 'ppb' (parts per billion) and 'ppt' (parts per trillion) are recognised as language-dependent terms since the value of billion and trillion can vary from language to language. SI therefore recommends avoiding these terms [1]. However, no alternative is suggested by the International Bureau of Weights and Measures (BIPM).

Roman type has two separate meanings in typography, both of which refer to the fact that the capital letters of a Roman font have an appearance similar to those used for lettering stone in ancient Rome: Roman type can refer to one of the major families of traditional typefaces as... In typography, italic type /tælk/ or /atælk/ refers to cursive typefaces based on a stylized form of calligraphic handwriting. ... Minuscule, or lower case, is the smaller form (case) of letters (in the Roman alphabet: a, b, c, ...). Originally alphabets were written entirely in majuscule (capital) letters which were spaced between well-defined upper and lower bounds. ... This article is about pressure in the physical sciences. ... Blaise Pascal (pronounced ), (June 20 [[1624 // ]] – August 19, 1662) was a French mathematician, physicist, and religious philosopher. ... The former Weights and Measures office in Middlesex, England. ... For other uses, see Pascal. ... The litre or liter (see spelling differences) is a unit of volume. ... The following is a list of sovereign states and territories where English is an official language, in order of population. ... NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, never GCWM). ... Also: 1979 by Smashing Pumpkins. ... A standards organization, also sometimes referred to as a standards body, a standards development organization or SDO (depending on what is being referenced), is any entity whose primary activities are developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise maintaining standards that address the interests of a wide base of... The litre or liter (see spelling differences) is a unit of volume. ... NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ... English grammar is a body of rules specifying how meanings are created in English. ... An inductor. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... This article is about the SI unit of frequency. ... The siemens (symbol: S) is the SI derived unit of electric conductance. ... The decimal separator is a symbol used to mark the boundary between the integral and the fractional parts of a decimal numeral. ... A space is a punctuation convention for providing interword separation in some scripts, including the Latin, Greek, Cyrillic, and Arabic. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, never GCWM). ... The decimal separator is a symbol used to mark the boundary between the integral and the fractional parts of a decimal numeral. ... A full stop or period (sometimes stop, full point, decimal point, or dot), is the punctuation mark commonly placed at the end of several different types of sentences in English and many other languages. ... The term comma has various uses; comma is the name used for one of the punctuation symbols: , The term comma is also used in music theory for various small intervals that arise as differences between approximately equal intervals. ... Most of the many languages of Europe belong to the Indo-European language family. ... An interpunct · is a small dot used for interword separation in ancient Latin script, being perhaps the first consistent visual representation of word boundaries in written language. ... A solidus, oblique or slash, /, is a punctuation mark. ... In mathematics, exponentiation is a process generalized from repeated multiplication, in much the same way that multiplication is a process generalized from repeated addition. ... A 104-key PC US English QWERTY keyboard layout The Dvorak Simplified Keyboard layout A standard Hebrew keyboard showing both Hebrew and QWERTY. A computer keyboard is a peripheral partially modelled after the typewriter keyboard. ... This article is mainly about the spoken Korean language. ... CJK is a collective term for Chinese, Japanese, and Korean, which comprise the main East Asian languages. ... The Unicode Standard, Version 5. ... The long and short scales are two different numerical systems used throughout the world: Short scale is the English translation of the French term échelle courte. ... The long and short scales are two different numerical systems used throughout the world: Short scale is the English translation of the French term échelle courte. ... The International Bureau of Weights and Measures is the English name of the Bureau international des poids et mesures (BIPM, often written in English Bureau International des Poids et Mesures), a standards organisation, one of the three organizations established to maintain the International System of Units (SI) under the terms...

Spelling variations

  • The official US spellings for "deca" and "metre" is "deka" and "meter" respectively.[13]
  • In some English-speaking countries, the unit "ampere" is often shortened to amp (singular) or amps (plural) in informal writing.

Conversion factors

The relationship between the units used in different systems is determined by convention or from the basic definition of the units. Conversion of units from one system to another is accomplished by use of a conversion factor. There are several compilations of conversion factors; see, for example Appendix B of NIST SP 811.[8] Conversion of units refers to conversion factors between different units of measurement for the same quantity. ...


Length, mass and temperature convergence

Specific gravity is commonly expressed in SI units or in reference to water. Since a cube with sides of 1 dm has volume of 1 dm3, which is 1 L and, when filled with water, has a mass of 1 kg, water has an approximate specific gravity of 1 kg/L, which is equal to 1 g/cm3 and 1 t/m3, and will freeze at 0 °C at 1 atmosphere of pressure. The litre or liter (see spelling differences) is a unit of volume. ...


Note that this is only an approximate definition of the kg, as the volume of water can change with temperature; the actual definition is based on a specific platinum-iridium cylinder held in a vault at the BIPM in Sèvres, France.


Cultural issues

The worldwide adoption of the metric system as a tool of economy and everyday commerce was based to some extent on the lack of customary systems in many countries to adequately describe some concepts, or as a result of an attempt to standardise the many regional variations in the customary system. International factors also affected the adoption of the metric system, as many countries increased their trade. Scientifically, it simplifies dealing with very large and small quantities since it lines up so well with the decimal numeral system. For other uses, see Decimal (disambiguation). ... This article is about different methods of expressing numbers with symbols. ...


Many units in everyday and scientific use are not derived from the seven SI base units (metre, kilogram, second, ampere, kelvin, mole, and candela) combined with the SI prefixes. In some cases these deviations have been approved by the BIPM.[14] Some examples include:

  • The many units of time — minute (min), hour (h), day (d) — in use besides the SI second, and are specifically accepted for use according to table 6.[15]
  • The year is specifically not included but has a recommended conversion factor.[16]
  • The Celsius temperature scale; kelvins are rarely employed in everyday use.
  • Electric energy is often billed in kilowatt-hours instead of megajoules.
  • The nautical mile and knot (nautical mile per hour) used to measure travel distance and speed of ships and aircraft (1 International nautical mile = 1852 m or approximately 1 minute of latitude at the equator). In addition to these, Annex 5 of the Convention on International Civil Aviation permits the "temporary use" of the foot for altitude.
  • Astronomical distances measured in astronomical units, parsecs, and light-years instead of, say, petametres (a light-year is about 9.461 Pm or about 9 461 000 000 000 000 m).
  • Atomic scale units used in physics and chemistry, such as the ångström, electronvolt, atomic mass unit and barn.
  • Some physicists still use the centimetre-gram-second (CGS) units, with their associated non-SI electric units.
  • In some countries the informal cup measurement has become 250 ml. Likewise, a 500 g "metric pound" is used in many countries. Liquids, especially alcoholic ones, are often sold in units whose origins are historical (for example, beer in pints in the UK, champagne in Jeroboams in France).
  • In the US blood glucose measurements are recorded in milligrams per decilitre (mg/dL); in Canada, Australia, New Zealand, Oceania and Europe, the standard is millimole per litre (mmol/L) or mM (millimolar).
  • Blood pressure is measured in mmHg instead of Pa.

The fine-tuning that has happened to the metric base-unit definitions over the past 200 years, as experts have tried periodically to find more precise and reproducible methods, does not affect the everyday use of metric units. Since most non-SI units in common use, such as the US customary units, are nowadays defined in terms of SI units, any change in the definition of the SI units results in a change of the definition of the older units, as well. For other uses, see Celsius (disambiguation). ... Electrical energy can refer to several closely related things. ... The watt-hour (symbol W·h) is a unit of energy. ... A nautical mile or sea mile is a unit of length. ... A knot is a unit of speed, abbreviated kt or kn. ... The Convention on International Civil Aviation, also known as the Chicago Convention, established the International Civil Aviation Organization (ICAO), a specialized agency of the United Nations charged with coordinating and regulating international air travel. ... A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, ′ – a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ... Altitude is the elevation of an object from a known level or datum. ... Astronomical distances are simply so massively huge as to defy the imagination and boggle the mind. ... The astronomical unit (AU or au or a. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... An ångström or aangstroem (the official transliteration), or angstrom (symbol Å) is a non-SI unit of length that is internationally recognized, equal to 0. ... The electronvolt (symbol eV) is a unit of energy. ... The unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic and molecular masses. ... A barn (symbol b) is a unit of area. ... Not to be confused with physician, a person who practices medicine. ... This article or section is in need of attention from an expert on the subject. ... The cup is a unit of measurement for volume, used in cooking to measure bulk foods, such as chopped vegetables (dry measurement), and liquids (fluid measurement). ... Look up pound in Wiktionary, the free dictionary. ... The pint is an English unit of volume or capacity in the imperial system and United States customary units, equivalent in each system to one half of a quart, and one eighth of a gallon. ... This article does not cite any references or sources. ... In medicine, blood sugar is a term used to refer to levels of glucose in the blood. ... A sphygmomanometer, a device used for measuring arterial pressure. ... One way of defining pressure is in terms of the height of a column of fluid that may be supported by that pressure; or the height of a column of fluid that exerts that pressure at its base. ... The U.S. customary units (more commonly known in the US as English units or standard units) are the non-metric units of measurement that are presently used in the United States, in some cases alongside the metric system of units. ...


Trade

The European Union has a directive[17] banning non-SI markings after 31 December 2009 on any goods imported into the European Union. This applies to all markings on products, enclosed directions and papers, packaging and advertisements. However, on September 11, 2007, the EU announced that the United Kingdom would be excepted from this directive and Imperial measurements would still be permitted indefinitely alongside with the metric system as supplementary indications.[18] is the 365th day of the year (366th in leap years) in the Gregorian calendar. ... 2009 (MMIX) will be a common year starting on Thursday of the Gregorian calendar. ... is the 254th day of the year (255th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... This article is about post-1824 imperial units, see also English unit, U.S. customary units or Avoirdupois. ...


See also


Organisations

Standards and conventions

References

  1. ^ Bureau International des Poids et Mesures
  2. ^ Official BIPM defintions
  3. ^ "In the International System of Units (SI) (BIPM, 2006), the definition of the meter fixes the speed of light in vacuum c0, the definition of the ampere fixes the magnetic constant (also called the permeability of vacuum) μ0, and the definition of the mole fixes the molar mass of the carbon 12 atom M(12C) to have the exact values given in the table [Table 1, p.7]. Since the electric constant (also called the permittivity of vacuum) is related to μ0 by ε0 = 1/μ0c02, it too is known exactly." CODATA report
  4. ^ The above remarks are a quote from Bureau International des Poids et Mesures SI Units brochure p. 111
  5. ^ The name "kilogram". Retrieved on 2006-07-25.
  6. ^ Barry N. Taylor & Ambler Thompson Ed. [2008]. The International System of Units (SI). Gaithersburg, MD: National Institute of Standards and Technology, 23. Retrieved on 2008-6-18. 
  7. ^ a b Bureau International des Poids et Mesures (2006). "The International System of Units (SI)". 8th ed.. Retrieved on 2008-02-13. Chapter 5.
  8. ^ a b Ambler Thompson & Barry N. Taylor (2008). "NIST Special Publication 811: Guide for the Use of the International System of Units (SI)". National Institute of Standards and Technology. Retrieved on 2008-06-18.
  9. ^ James M. Turner (2008-5-9). "Interpretation of the International System of Units (the Metric System of Measurement) for the United States". Government Printing Office. Retrieved on 2008-06-18.
  10. ^ Taylor, B. N.. NIST Guide to SI Units - Rules and Style Conventions. National Institute of Standards and Technology. Retrieved on 2007-04-12.
  11. ^ The International System of Units (SI). International Bureau of Weights and Measures (BIPM). Retrieved on 2008-04-18.
  12. ^ Barry N. Taylor, Ed. [2001]. The International System of Units (SI). Washington, DC: National Institute of Standards and Technology, 30. Retrieved on 2007-10-15. 
  13. ^ The International System of Units iii. Retrieved on 2008-05-27.
  14. ^ BIPM - Table 8
  15. ^ BIPM - Table 6
  16. ^ NIST Guide to SI Units - Appendix B9. Conversion Factors
  17. ^ Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to units of measurement and on the repeal of Directive 71/354/EEC, as amended with Directive 89/617/EEC (which changed the cutoff date in article 3.2 to 31 December 1999) and Directive 1999/103/EC (which further changed the date to 31 December 2009). Retrieved on 2006-07-24.
  18. ^ BBC NEWS | UK | EU gives up on 'metric Britain'

Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 206th day of the year (207th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 44th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 169th day of the year (170th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 169th day of the year (170th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 102nd day of the year (103rd in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 108th day of the year (109th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 288th day of the year (289th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 147th day of the year (148th in leap years) in the Gregorian calendar. ... is the 365th day of the year (366th in leap years) in the Gregorian calendar. ... Events of 2008: (EMILY) Me Lesley and MIley are going to China! This article is about the year. ... is the 365th day of the year (366th in leap years) in the Gregorian calendar. ... 2009 (MMIX) will be a common year starting on Thursday of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 205th day of the year (206th in leap years) in the Gregorian calendar. ...

Further reading

IUPAC logo The International Union of Pure and Applied Chemistry (IUPAC) (Pronounced as eye-you-pack) is an international non-governmental organization established in 1919 devoted to the advancement of chemistry. ... Quantities, Units and Symbols in Physical Chemistry (ISBN 0632035838), also known as the Green Book, edited by I. Mills, et al. ...

External links

Official
Information
History
  • LaTeX SIunits package manual gives a historical background to the SI system.
Research
Pro-metric pressure groups
Pro-customary measures pressure groups

The Open Directory Project (ODP), also known as dmoz (from , its original domain name), is a multilingual open content directory of World Wide Web links owned by Netscape that is constructed and maintained by a community of volunteer editors. ... This article is about political advocates. ... The Open Directory Project (ODP), also known as dmoz (from , its original domain name), is a multilingual open content directory of World Wide Web links owned by Netscape that is constructed and maintained by a community of volunteer editors. ...


  Results from FactBites:
 
The International System of Units, by Robert A. Nelson (6282 words)
In Paris the unit of length was the Pied de Roi and the unit of mass was the Livre poids de marc.
The unit of volume, the pinte (later renamed the litre), was defined as the volume of a cube having a side equal to one-tenth of a meter.
The unit of mass, the grave (later renamed the kilogramme), was defined as the mass of one pinte of distilled water at the temperature of melting ice.
International System of Units - Wikipedia, the free encyclopedia (1800 words)
The International System of Units (abbreviated SI from the French language name Système international d'unités) is the modern form of the metric system.
The metric system was conceived by a group of scientists (among them, Lavoisier) which had been commissioned by king Louis XVI of France to create a unified and rational system of measures.
Since most non-SI units in common use, such as the U.S. customary units, are nowadays defined in terms of SI units, any change in the definition of the SI units results in a change of the definition of the older units as well.
  More results at FactBites »

 
 

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WhitneyBOWERS23
17th August 2010
I would like to propose not to hold off until you earn enough money to buy all you need! You should get the business loans or just collateral loan and feel fine

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