The United States protoype kilogram kept at the U.S. National Institute of Standards and Technology. In 1889 the International Bureau of Weights and Measures (BIPM) accepted 40 kilogram prototypes.1 One was handed to the national laboratories of each member state of the Metre Convention to serve as national standards, one served as the international prototype kilogram held at the BIPM laboratory2 in Sèvres, France and the remainder were kept as working copies or as spares. The metric system is an international decimalised system of measurement, first adopted by France in 1791, that is the common system of measuring units used by most of the world. It exists in several variations, with different choices of fundamental units, though the choice of base units does not affect its day-to-day use. Over the last two centuries, different variants have been considered the metric system. Since the 1960s the International System of Units ("Système international d'unités" in French, hence "SI") has been the internationally recognised standard metric system. Metric units are universally used in scientific work, and widely used around the world for personal and commercial purposes. A standard set of prefixes in powers of ten may be used to derive larger and smaller units from the base units. According to the American Central Intelligence Agency's Factbook, the International System of Units is the official system of measurement for all nations in the world except for Myanmar, Liberia, and the United States.3 (Some sources, though, identify Liberia as metric.456) However, a number of other jurisdictions have laws mandating or permitting other systems of measurement in some or all contexts, such as the United Kingdom – where for example the traffic sign regulations (TSRGD) only allow distance signs displaying imperial units (miles or yards)7 – or Hong Kong.8 In the United States, metric units are widely used in science, military, and partially in industry, but customary units predominate in household use. At retail stores, the litre is a commonly used unit for volume, especially on bottles of beverages, and milligrams are used to denominate the amounts of medications, rather than grains. Also, other standardised measuring systems other than metric are still in universal international use, such as nautical miles and knots in international aviation. Contents 1 Overview 2 History 3 Replicable prototypes 4 Decimal multiples 5 Prefixes 6 Practicality 7 Coincidental similarities 8 Metric systems 8.1 Original system 8.2 Centimetre-gram-second systems 8.3 Metre-kilogram-second systems 8.4 Metre-tonne-second systems 8.5 Millimetre-newton-second systems 8.6 Gravitational systems 9 Variations in English spelling 10 Conversion and calculation errors 11 See also 12 Notes and references 13 External links Overview Countries which have officially adopted the metric system (green). Only three nations out of 203 have not officially adopted the International System of Units as their primary or sole system of measurement: Burma, Liberia, and the United States of America.9 The United States is the only industrialised country in the world that has an aversion to using the International System of Units as its predominant system of measurement.10 One goal of the metric system is to have a single unit for every physical quantity; another important one is to avoid the need for conversion factors when making calculations with physical quantities. All lengths and distances, for example, are measured in metres, or thousandths of a metre (millimetres), or thousands of metres (kilometres), and so on. There is no profusion of different units with different conversion factors, such as inches, feet, yards, fathoms, rods, chains, furlongs, miles, nautical miles, leagues, etc. Multiples and submultiples are related to the fundamental unit by factors of powers of ten, so that one can convert by simply moving the decimal place: 1.234 metres is 1234 millimetres, 0.001234 kilometres, etc. The use of fractions, such as 2⁄7 of a metre, is not prohibited, but uncommon, as it is generally not necessary.

However decimal time is not used. Submultiples of the second (the microsecond for example) are used in scientific work but for lengths of time greater than a second traditional units (minutes, hours, days ...) with their non-decimal conversion factors, are almost always used rather than, say, "megaseconds". In the late 18th century, Louis XVI of France charged a group of experts to develop a unified, natural and universal system of measurement to replace the disparate systems then in use. This group, which included such notables as Lavoisier, produced the metric system, which was then adopted by the revolutionary government of France. On 13 July 1790 Thomas Jefferson presented a document Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States to congress in which he advocated a decimal system that used traditional names for units (such as ten inches per foot). The report was considered but not adopted by Congress. In the early metric system, there were several fundamental or base units, the grad or grade for angles, the metre for length, the gram for mass and the litre for capacity. These were derived from each other via the properties of natural objects, mainly the Earth and water: 1 metre was originally defined as 1⁄10,000,000 of the distance between the North Pole and Earth's equator as measured along the meridian passing through Paris, the kilogram was originally defined as the mass of one litre (or, equivalently, 1 dm3) of water at its melting point (this definition was later revised to specify a temperature of 4 °C). The Celsius temperature scale was derived from the properties of water, with 0 °C being defined as its freezing point and 100 °C being defined as its boiling point under a pressure of one standard atmosphere. The metre was later redefined as the length of a particular bar of platinum-iridium alloy; then in terms of the wavelength of light emitted by a specified atomic transition; and now is defined as the distance travelled by light in an absolute vacuum during 1⁄299,792,458 of a second. The gram, originally one millionth of the mass of a cubic metre of water, is currently defined by one thousandth of the mass of a specific object that is kept in a vault in France; however there are efforts under way to redefine it in terms of physical quantities that could be reproduced in any laboratory with suitable equipment. The second, originally 1⁄86,400 of the mean solar day, was redefined in 1967 to be 9,192,631,770 periods of vibration of the radiation emitted at a specific wavelength by an atom of caesium-133. Varying choices have been made for the fourth base unit, which is needed to define electrical and magnetic units. The International System of Units uses the ampere, the base unit of electric current. Other quantities are derived from the base units; for example, the basic unit of speed is metres per second. As each new definition is introduced, it is designed to match the previous definition as precisely as possible, so these changes of definition have not affected most practical applications. (See SI and individual unit articles for full definitions.) The names of multiples and submultiples are formed with prefixes. They include kilo- (thousand, 103), centi- (hundredth, 10−2) and milli- (thousandth, 10−3). The most commonly used prefixes for multiples depend on the application and sometimes tradition. For example, long distances are normally stated in thousands of kilometres, not megametres, while, for example, the farad, the base unit of electrical capacitance, is a very large unit so that smaller units such as picofarads and nanofarads are more often encountered.

Most everyday users of the metric system measure temperature in degrees Celsius, though the SI unit is the kelvin, a scale whose units have the same "size", but which starts at absolute zero. Zero degrees Celsius equals 273.15 kelvins (the word "degree" is no longer to be used with kelvins since 1967-68). Angular measurements have been decimalised, but the older non-decimal units of angle are far more widely used. The decimal unit, which is not part of SI, is the gon or grad, equal to one hundredth of a right angle. Subunits are named, rather than prefixed: the gon is divided into 100 decimal minutes, each of 100 decimal seconds. The traditional system, originally Babylonian, has 360 degrees in a circle, 60 minutes of arc (also called arcminutes) in a degree, and 60 seconds of arc (also called arcseconds) in a minute. The clarifier "of arc" is dropped if it is clear from the context that we are not speaking of minutes and seconds of time. Sometimes angles are given as decimal degrees, e.g., 26.4586 degrees, or in other units such as radians (especially in mathematical and scientific uses other than astronomy) or angular mils. History Countries by date of metrication. Colours red to green show the pattern of metrication from 1795 to 1998. Black identifies countries that have not adopted the metric system as the primary measurement system. White identifies countries that already used the metric system at the time they gained their independence. See also: Metrication Adoption of the metric system by the various countries, or metrication, is shown by year on the attached map. In 1586, the Flemish mathematician Simon Stevin published a small pamphlet called De Thiende ("the tenth"). Decimal fractions had been employed for the extraction of square roots some five centuries before his time, but nobody used decimal numbers in daily life. He felt that this innovation was so significant that he declared the universal introduction of decimal coinage, measures, and weights to be merely a question of time. The idea of a metric system has been attributed to John Wilkins, first secretary of the Royal Society of London in 1668.111213 The idea did not catch on, and England continued with its existing system of various weights and measures. In 1670, Gabriel Mouton, a French abbot and scientist, proposed a decimal system of measurement based on the circumference of the Earth. His suggestion was a unit, milliare, that was defined as a minute of arc along a meridian. He then suggested a system of sub-units, dividing successively by factors of ten into the centuria, decuria, virga, virgula, decima, centesima, and millesima. His ideas attracted interest at the time, and were supported by both Jean Picard and Christiaan Huygens in 1673, and also studied at the Royal Society in London. In the same year, Gottfried Leibniz independently made proposals similar to those of Mouton. The proliferation of disparate measurement systems was one of the most frequent causes of disputes amongst merchants and between citizens and tax collectors. A unified country with a single currency and a countrywide market, as most European countries were becoming by the end of the 18th century, had a very strong economic incentive to break with this situation and standardise on a measuring system. The inconsistency problem was not one of different units but one of differing sized units. Instead of simply standardising the size of the existing units, the leaders of the French revolutionary Assemblée Constituante decided that a completely new system should be adopted. It was felt that no country would accept standardising on the units of another country, but that there would be less resistance if a completely new system made change compulsory for all countries.citation needed Metric seal

On 20 May 1875 an international treaty known as the Convention du Mètre (Metre Convention) was signed by 17 states. This treaty established the following organisations to conduct international activities relating to a uniform system for measurements: Conférence générale des poids et mesures (CGPM), an intergovernmental conference of official delegates of member nations and the supreme authority for all actions; Comité international des poids et mesures (CIPM), consisting of selected scientists and metrologists, which prepares and executes the decisions of the CGPM and is responsible for the supervision of the International Bureau of Weights and Measures; Bureau international des poids et mesures (BIPM), a permanent laboratory and world centre of scientific metrology, the activities of which include the establishment of the basic standards and scales of the principal physical quantities and maintenance of the international prototype standards. Replicable prototypes The usual way to establish a standard was to make prototypes of the base units and distribute copies. This would make the new standard reliant on the original prototypes, which would be in conflict with the previous goal, since all countries would have to refer to the one holding the prototypes. Instead, the designers developed definitions of the base units such that any laboratory equipped with proper instruments should be able to make their own models of them. The original base units of the metric system could be derived from the length of a meridian arc of the Earth and the weight of a certain volume of pure water. For a time, the Assemblée Constituante considered using the length of a pendulum beating the second in Paris as the base of the metre; when they heard that the British Parliament was discussing a similar proposal, based on the length of the pendulum beating the second in London, the Assemblée contacted their counterparts in London and offered to standardise on the London pendulum. Instead, the UK abandoned the idea of metrication for another two centuries, and the meridian definition of the metre was adopted.14 The pendulum was not a likely choice for a prototype in any case, since its period (or, inversely, the length of the string holding the bob for the same period) changes around the Earth. Likewise, they discarded using the circumference of the Earth over the Equator since not all countries have access to the Equator while all countries have access to a section of a meridian.citation needed Decimal multiples The metric system is decimal, in the sense that all multiples and submultiples of the base units are factors of powers of ten of the unit. Fractions of a unit are not used formally. The practical benefits of a decimal system are such that it has been used to replace other non-decimal systems outside the metric system of measurements; for example currencies. The simplicity of decimal prefixes encouraged the adoption of the metric system; the usage of base 10 arithmetic aids in unit conversion, as compared to 12 inches per foot, 3 feet per yard, et cetera. At most, differences in expressing results are simply a matter of shifting the decimal point or changing an exponent; for example, the speed of light may be expressed as 299,792.458 km/s or 2.99792458×108 m/s. Prefixes Main article: SI prefix All derived units would use a common set of prefixes for each multiple. Thus the prefix kilo could be used for mass (kilogram) or length (kilometre) both indicating a thousand times the base unit. This did not prevent the popular use of names for some derived units such as the tonne which is a megagram; derived from old customary units and rounded to metric.

The function of the prefix is to multiply or divide the measure by a factor of ten, one hundred or a positive integer power of one thousand.15 If the prefix is Greek-derived, the measure is a positive power. If the prefix is Latin-derived, it is a negative power, except by 10−6 (micro~) which is also Greek-derived. Later SI extensions to the prefix system did not follow the Greek-greater-than-one/Latin-less-than-one convention. metre Unit Relation to base kilometre 103 metres hectometre 102 metres decametre 101 metres metre decimetre 10−1 metres centimetre 10−2 metres millimetre 10−3 metres litre Unit Relation to base kilolitre 103 litres hectolitre 102 litres decalitre 101 litres litre decilitre 10−1 litres centilitre 10−2 litres millilitre 10−3 litres The prefix kilo~ is of Greek origin, while the prefixes centi~ and milli~ are of Latin origin, and these three are the most familiar ones from everyday use. Similarly, the other metric measurements also use prefixes rooted in Latin and Greek: deci- comes from Latin, while nano-, micro-, deka-, hecto-, mega-, giga- have been borrowed from Greek. Practicality The base units were chosen to be of similar magnitude to customary units.citation needed The metre, being close to half a toise (French yard equivalent), became more popular than the failed decimal hour of the Republican Calendar which was 2.4 times the normal hour. The kilometre was originally defined as the length of an arc spanning a decimal minute of latitude, a similar definition to that of the nautical mile which was the length of an arc of one (non-decimal) minute of latitude. Originally, units for volume and mass were directly related to each other, with mass defined in terms of a volume of water. Even though that definition is no longer used, the relation is quite close at room temperature (1 litre is ≈ .9971 kg at 20 degrees Celsius.16) and nearly exact at 4 °C. So as a practical matter, one can fill a container with water and weigh it to get the volume. For example, 1 kilolitre = 1 cubic metre ≈ 1 tonne of water 1 litre = 1 cubic decimetre ≈ 1 kilogram of water 1 millilitre = 1 cubic centimetre ≈ 1 gram of water 1 microlitre = 1 cubic millimetre ≈ 1 milligram of water Coincidental similarities Two important values, when they were expressed in the metric system, turned out to be very close to a power of 10. The standard acceleration due to gravity on Earth, gn, has been defined to be 9.80665 m/s2 exactly. Accordingly the force exerted on a mass of one kilogram in Earth gravity (F = m·a) is about 10 newtons (kg·m/s2). This simplified the metrication of many machines such as locomotives, which were simply re-labelled from, e.g., 85 tonnes (i.e., tonne-force) to 850 kN. A closer approximation is π2 (≈ 9.86960) m/s2, which means a seconds pendulum is almost one metre long. Also, the standard atmospheric pressure, previously expressed in atmospheres, when given in pascals, is 101.325 kPa. Since the difference between 10 atmospheres and 1 MPa is only 1.3%, many devices were simply re-labelled by dividing the scale by ten (e.g., 1 atm was changed to 0.1 MPa). In addition, the speed of light in a vacuum turned out to be close (0.07% different) to 3×108 m/s; the exact value, 299792458, has since become the definition. The distance of a Light Year is close to 10 Trillion kilometres (1016 metres or 1013 km).

A useful conversion used in meteorology is 1 m/s ≈ 2 knots, or actually 1.94384 kn (3% error).17 Metric systems Original system The metric system, including the metre, was first fully described by Englishman John Wilkins in 1668 in a treatise presented to the Royal Society, some 120 years before the French adopted the system. It is believed that the system was transmitted to France from England by Benjamin Franklin (who spent a great deal of time in London), and produced the by-product of the decimalised paper currency system, before finding favour with American revolutionary ally Louis XVI.18 The original French system continued the tradition of having separate base units for geometrically related dimensions, e.g., metre for lengths, are (100 m2) for areas, stère (1 m3) for dry capacities, and litre (1 dm3) for liquid capacities. The hectare, equal to a hundred ares, is the area of a square 100 metres on a side (about 2.47 acres), and is still in use. The early metric system included only a few prefixes from milli (one thousandth) to myria (ten thousand), and they were based on powers of 10 unlike later prefixes added in the SI, which are based on powers of 1,000. The base unit of mass is the kilogram. This is the only base unit that has a prefix, for historical reasons. Originally the kilogram was called the "grave", and the "gram" was an alternative name for a thousandth of a grave. After the French Revolution, the word "grave" carried negative connotations, as a synonym for the title "count". The grave was renamed the kilogram.19 Several national variants existed thereof with aliases for some common subdivisions. In general, this entailed a redefinition of other units in use (e.g., 500-gram pounds or 10-kilometre miles or leagues). An example of these is mesures usuelles. However, it is debatablewho? whether such systems are true metric systems.clarification neededcitation needed Centimetre-gram-second systems Early on in the history of the metric system, various versions of centimetre gram second system of units (CGS) had been in use. These units were particularly convenient in science and technology. For example, in CGS the density of water is approximately one gram per cubic centimetre. Metre-kilogram-second systems Later metric systems were based on the metre, kilogram and second (MKS) to improve the value of the units for practical applications. Metre-kilogram-second-coulomb (MKSC) and metre-kilogram-second-ampere (MKSA) systems are extensions of these. The International System of Units (System international units or SI) is the current international standard metric system and the system most widely used around the world. It is based on the metre, kilogram, second, ampere, kelvin, candela and mole. Proposals have been made to change the definitions of four of the base units at the 24th meeting of the CGPM in October 2011. These changes should not affect the average person.20 Metre-tonne-second systems The metre-tonne-second system of units (MTS) was based on the metre, tonne and second. It was invented in France and mostly used in the Soviet Union from 1933 to 1955. Millimetre-newton-second systems This system is based on the millimetre, newton and second. It is used in simulation of mechanical systems using tools like finite element solvers. The geometry, loading and time are all convenient, common and intuitive. A consequence of this is that the density term is in mega-grams per cubic millimetre. To convert from g/cm3, a common unit for density, requires multiplication by 109. Gravitational systems

Gravitational metric systems use the kilogram-force (kilopond) as a base unit of force, with mass measured in a unit known as the hyl, TME, mug or metric slug. Note these are not part of the International System of Units (SI). Variations in English spelling Although the symbol for the kilometre throughout the world is "km", there is no consistency in the spelling of the name "kilometre". Variants include Chilometro (Italian), Kilometer (German), kilometre (French), χιλιόμετρο (Greek), quilómetro (Portuguese) and Километър (Bulgarian).21 Similar variations are found with the spelling of other units of measure in various countries including differences in American English and British spelling. For example meter and liter are used in the United States whereas metre and litre are used in the United Kingdom. In addition, the official US spelling for the rarely used SI prefix for ten is deka. In American English the term metric ton is the normal usage whereas in other varieties of English tonne is common. The US government has approved this terminology for official use. In scientific contexts, only the symbols are used;citation needed since these are universally the same, the differences do not arise in practice in scientific use. Gram is also sometimes spelled gramme in English-speaking countries other than the United States, though it is an older spelling and its usage is declining. The useage of some prefixes to refer to a specific unit differs amongst English-speaking nations. For example a speaker of British English would ensure the bag they were taking on a flight was under 20 "kilos" (kg), while a speaker of Indian English would want their bag to be under 20 "kay gees" (kg) but would take a taxi to the airport because it is 15 "kilos" (km) out of town. Conversion and calculation errors The dual usage of metric and conventional units in the United States can sometimes result in serious errors. According to the National Transportation Safety Board, the confusion between pounds and kilograms means that aircraft are sometimes overloaded,22 and the Institute for Safe Medication Practices has reported that confusion between grains and grams is sometimes the reason for medical errors. One example given is a case where a patient received phenobarbital 0.5 grams instead of 0.5 grains (0.03 grams) after the prescriber misread the prescription.23 Two major examples of accidents caused by unit confusion are the Canadian "Gimli Glider" accident in 1983, when a Boeing 767 jet ran out of fuel in mid-flight because of two mistakes in figuring the fuel supply of Air Canada's first aircraft to use metric measurements,24 and NASAs 1999 loss of the $125 million Mars Climate Orbiter because one engineering team used metric units while another used US customary units for a calculation.25 See also Conversion of units French units of measurement History of measurement International system of units ISO/IEC 80000, style manual for measurements metric and non metric, superseding ISO 31 Mesures usuelles (French: customary measurements), a compromise between metric and traditional units employed until 1839 Metric time Metrication, the process of introducing the SI metric system as the worldwide standard for physical measurements (a long-term series of independent and systematic conversions from the various separate local systems of weights and measures) Antimetrication Metrication Board Metric Martyrs Metrology SI prefix IEC Binary Prefixes, used in computer science Units of measurement Notes and references ^ "NPL's Beginner's Guide to Mass". Teddington, United Kingdom: National Physical Laboratory. http://www.npl.co.uk/educate-explore/factsheets/mass/mass-(poster). Retrieved 2011-02-06.  ^ [1] ^ The World Factbook. (2006). Washington: Central Intelligence Agency. Retrieved 8 August 2006 from Appendix G. ^ "African Development Bank - World Bank Joint Assistance Strategy 2008-2011 and eligibility to the Fragile States Facility". PDF Document. African Development Bank. November 2008. p. i. http://www.afdb.org/fileadmin/uploads/afdb/Documents/Project-and-Operations/Liberia_%20JAS%20BAD-WB%202008-2011%20Eligibility%20to%20the%20Fragile%20States%20Facility.pdf. Retrieved 24 April 2010.  ^ Dr. Michael D. Wilcox, Jr. Department of Agricultural Economics University of Tennessee (2008). "Reforming Cocoa and Coffee Marketing in Liberia". Presentation and Policy Brief. University of Tennessee. http://trend.ag.utk.edu/international/ReformingCocoaCoffeeMarketingLiberia.pdf. Retrieved 25 April 2010.  ^ http://www.cl.cam.ac.uk/~mgk25/metric-system-faq.txt ^ "Statutory Instrument 2002 No. 3113 The Traffic Signs Regulations and General Directions 2002". Her Majesty's Stationery Office (HMSO). 2002. http://www.opsi.gov.uk/si/si2002/20023113.htm. Retrieved 18 March 2010.  ^ HK Weights and Measures Ordinance ^ http://www.nist.gov/ts/wmd/metric/upload/1136a.pdf ^ http://metricviews.org.uk/2010/01/will-the-european-commission-challenge-us-labelling-rules/ ^ An Essay towards a Real Character and a Philosophical Language (Reproduction) ^ An Essay towards a Real Character and a Philosophical Language (Transcription) ^ Metric system 'was British' - from the BBC video news ^ Roland Mousnier, Progrès Scientifique et Technique au XVIII Siècle, Librairie Plon, Paris 1958. ^ The factor ten thousand was also once used. The corresponding prefixes myria~ 104 and myrio~ 10-4 were both Greek-derived. ^ http://www.wolframalpha.com/input/?i=mass+of+1L+of+water+at+room+temperature ^ Bureau International des Poids et Mesures (March 2006). "The International System of Units (SI) (Table 8)". 8th ed.. http://www.bipm.org/en/si/si_brochure/chapter4/table8.html. Retrieved 12 April 2007.  ^ John Wilkins. (1668) Pat Naughtin, transcriber. Real Character and a Philosophical Language. Selected pages republished by Metrication matters. Retrieved 3 August 2007. ^ Nelson, Robert A (February 2000). "The International System of Units: Its History and Use in Science and Industry". Applied Technology Institute. http://www.aticourses.com/international_system_units.htm. Retrieved 12 April 2007.  ^ Ian Mills (29 September 2010). "Draft Chapter 2 for SI Brochure, following redefinitions of the base units". CCU. http://www.bipm.org/utils/en/pdf/si_brochure_draft_ch2.pdf. Retrieved 2011-01-01.  ^ "Online Translation- Offering hundreds of dictionaries and translation in more than 800 language pairs". Babylon. http://translation.babylon.com/. Retrieved 2011-02-05.  ^ NTSB Order No. EA-4510, (1996), Washington, D.C.: National Transportation Safety Board. Retrieved August 3, 2008. ^ ISMP Medication Safety Alert, (April–June 1999), Institute for Safe Medication Practices. Retrieved 3 August 2008. ^ "Jet's Fuel Ran Out After Metric Conversion Errors". New York Times. July 30, 1983. http://select.nytimes.com/search/restricted/article?res=F00F17F73B5D0C738FDDAE0894DB484D81. Retrieved 21 August 2007. "Air Canada said yesterday that its Boeing 767 jet ran out of fuel in mid-flight last week because of two mistakes in figuring the fuel supply of the airline's first aircraft to use metric measurements. After both engines lost their power, the pilots made what is now thought to be the first successful emergency dead stick landing of a commercial jetliner."  ^ "NASA's metric confusion caused Mars orbiter loss". CNN. 30 September 1999. http://www.cnn.com/TECH/space/9909/30/mars.metric/. Retrieved 21 August 2007. "NASA lost a $125 million Mars orbiter because one engineering team used metric units while another used English units for a key spacecraft operation, according to a review finding released Thursday. For that reason, information failed to transfer between the Mars Climate Orbiter spacecraft team at Lockheed Martin in Colorado and the mission navigation team in California. Lockheed Martin built the spacecraft. "People sometimes make errors," said Edward Weiler, NASA's Associate Administrator for Space Science in a written statement."  External links CBC Radio Archives Talking about the history of Metric. v · d · eSystems and systems science Systems categories Systems theory · Systems science · Systems scientists (Conceptual · Physical · Social) Systems Biological · Complex · Complex adaptive · Conceptual · Database management · Dynamical · Economical · Ecosystem · Formal · Global Positioning System · Human anatomy · Information systems · Legal systems of the world · Systems of measurement · Metric system · Multi-agent system · Nervous system · Nonlinearity · Operating system · Physical system · Political system · Sensory system · Social structure · Solar System · Systems art Theoretical fields Chaos theory · Complex systems · Control theory · Cybernetics · Living systems · Sociotechnical systems theory · Systems biology · System dynamics · Systems ecology · Systems engineering · Systems psychology · Systems science · Systems theory Systems scientists

Russell L. Ackoff · William Ross Ashby · Béla H. Bánáthy · Gregory Bateson · Richard E. Bellman · Stafford Beer · Ludwig von Bertalanffy · Murray Bowen · Kenneth E. Boulding · C. West Churchman · George Dantzig · Heinz von Foerster · Jay Wright Forrester · George Klir · Edward Lorenz · Niklas Luhmann · Humberto Maturana · Margaret Mead · Donella Meadows · Mihajlo D. Mesarovic · James Grier Miller  · Howard T. Odum · Talcott Parsons · Ilya Prigogine · Anatol Rapoport · Claude Shannon · Francisco Varela · Kevin Warwick · Norbert Wiener · Anthony Wilden · Charles A S Hall v · d · eSystems of measurement Metric systems International System of Units · metre-kilogram-second · centimetre-gram-second · metre-tonne-second · gravitational system Natural units Geometric · Planck · Stoney · Lorentz–Heaviside · Schrödinger · Atomic · Electronic · Quantum chromodynamical Conventional systems Astronomical · Electrical · Temperature Customary systems Avoirdupois · Apothecaries' · British Empire · Burmese · Canadian · Chinese · Cornish · Danish · Dutch · English · Finnish · French · German · Hindu · Hong Kong · Irish · Japanese · Maltese · Norwegian · Pegu · Polish · Portuguese · Romanian · Russian · Scottish · Spanish · Swedish · Taiwanese · Tatar · Turkish · Troy · United States Ancient systems Greek · Roman · Egyptian · Hebrew · Arabic · Mesopotamian · Persian · Indian Other systems Non-standard · Mesures usuelles · N-body

Russell L. Ackoff · William Ross Ashby · Béla H. Bánáthy · Gregory Bateson · Richard E. Bellman · Stafford Beer · Ludwig von Bertalanffy · Murray Bowen · Kenneth E. Boulding · C. West Churchman · George Dantzig · Heinz von Foerster · Jay Wright Forrester · George Klir · Edward Lorenz · Niklas Luhmann · Humberto Maturana · Margaret Mead · Donella Meadows · Mihajlo D. Mesarovic · James Grier Miller  · Howard T. Odum · Talcott Parsons · Ilya Prigogine · Anatol Rapoport · Claude Shannon · Francisco Varela · Kevin Warwick · Norbert Wiener · Anthony Wilden · Charles A S Hall v · d · eSystems of measurement Metric systems International System of Units · metre-kilogram-second · centimetre-gram-second · metre-tonne-second · gravitational system Natural units Geometric · Planck · Stoney · Lorentz–Heaviside · Schrödinger · Atomic · Electronic · Quantum chromodynamical Conventional systems Astronomical · Electrical · Temperature Customary systems Avoirdupois · Apothecaries' · British Empire · Burmese · Canadian · Chinese · Cornish · Danish · Dutch · English · Finnish · French · German · Hindu · Hong Kong · Irish · Japanese · Maltese · Norwegian · Pegu · Polish · Portuguese · Romanian · Russian · Scottish · Spanish · Swedish · Taiwanese · Tatar · Turkish · Troy · United States Ancient systems Greek · Roman · Egyptian · Hebrew · Arabic · Mesopotamian · Persian · Indian Other systems Non-standard · Mesures usuelles · N-body

Russell L. Ackoff · William Ross Ashby · Béla H. Bánáthy · Gregory Bateson · Richard E. Bellman · Stafford Beer · Ludwig von Bertalanffy · Murray Bowen · Kenneth E. Boulding · C. West Churchman · George Dantzig · Heinz von Foerster · Jay Wright Forrester · George Klir · Edward Lorenz · Niklas Luhmann · Humberto Maturana · Margaret Mead · Donella Meadows · Mihajlo D. Mesarovic · James Grier Miller  · Howard T. Odum · Talcott Parsons · Ilya Prigogine · Anatol Rapoport · Claude Shannon · Francisco Varela · Kevin Warwick · Norbert Wiener · Anthony Wilden · Charles A S Hall v · d · eSystems of measurement Metric systems International System of Units · metre-kilogram-second · centimetre-gram-second · metre-tonne-second · gravitational system Natural units Geometric · Planck · Stoney · Lorentz–Heaviside · Schrödinger · Atomic · Electronic · Quantum chromodynamical Conventional systems Astronomical · Electrical · Temperature Customary systems Avoirdupois · Apothecaries' · British Empire · Burmese · Canadian · Chinese · Cornish · Danish · Dutch · English · Finnish · French · German · Hindu · Hong Kong · Irish · Japanese · Maltese · Norwegian · Pegu · Polish · Portuguese · Romanian · Russian · Scottish · Spanish · Swedish · Taiwanese · Tatar · Turkish · Troy · United States Ancient systems Greek · Roman · Egyptian · Hebrew · Arabic · Mesopotamian · Persian · Indian Other systems Non-standard · Mesures usuelles · N-body