metric system

Dictionary: metric system

A decimal system of units based on the meter as a unit length, the kilogram as a unit mass, and the second as a unit time.

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Sci-Tech Encyclopedia: Metric system

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A system of units used in scientific work throughout the world and employed in general commercial transactions and engineering applications in most of the developed nations of the world except for the United Kingdom and the United States. The basic units of the metric system define length (meter), mass (kilogram), and time (second).

The chief advantage of the metric system is that it is based on standards that have been accepted by international agreement, and it therefore provides a common basis for all scientific measurements. A second advantage of the metric system lies in the fact that only decimal multiples and submultiples of the fundamental length and mass units and of other derived units are employed. See also Physical measurement; Units of measurement.

Marketing Dictionary: metric system

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System of measuring size, weight, and volume, based upon decimal units. The basic metric system units are grams, meters, and liters. One gram = 0.035 ounce. One meter = 39.37 inches. One liter = 61.025 cubic inches (cubic capacity), 0.908 quart (dry measure), or 1.057 quarts (liquid measure).

All nations of the world with the exception of the United States and two very small countries use the metric system. The U.S. Reluctance to conform with these worldwide standards makes it difficult to market packaged goods globally. For example, a consumer abroad accustomed to buying in liter or gram quantities will not understand a package label that uses quarts or ounces. Also, food package recipes cannot be easily translated from teaspoons and cups to grams and liters as required for non-U.S. Cooking utensils. However, for international marketing, the expense of printing metric versions of labels and packages is a costly necessity.

Business Dictionary: Metric System

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Decimal system of weights and measures in which the gram, meter, and liter are the basic units of weight, length, and capacity, respectively. See also Metrication.

Food Lover's Companion: metric system

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A system of weights and measures that's used throughout much of the world. The basic units are the gram for weight and the meter for length. When calculating conversions, the same figure (0.236) is used whether converting to or from metric. The only difference is that, when converting to metric (as from cups to liters), you multiply the number of cups by 0.236 to get the equivalent in liters. When converting from metric (as from liters to cups), you divide the liters by 0.236 to get the cup equivalency.

Dental Dictionary: metric system

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A decimal system of weights and measures almost universally used in scientific and professional work, including the writing of prescriptions. The individual units are based on an international set of standards, notably the meter, liter, and kilogram.

Measures and Units: metric system

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The comprehensive decimal system created as a national standard in France in the 1790s, following the revolution, subsequently adopted on an international basis as the primary standard in many countries, and then the standard for science. It is now the primary system for measurement in virtually all developed countries other than the USA; even there it provides the official basis for the measurement standards as well as the scheme for most science. Today it has become the SI system, with various technical differences from its predecessor. Other manifestations include the c.g.s. system, the m.k.s. system, and an m.t.s. system. (Within general entries in this book, these are labelled Metric-c.g.s., Metric-m.k.s., and so on, sub-qualified where appropriate.)

History

The metric system grew out of proposals made at least as early as 1670, considered officially then enacted in post-revolutionary France in the 1790s, though not widely accepted until 1845. The initial fundamentals were a metre (symbolically m), equal in length to ¹/_10000000 of a meridional quadrant of Earth and a gramme (gram, symbolically g), equal to the mass of ¹/_1000000 cubic metre of water (at normal atmospheric pressure and the temperature of its maximum volumic mass, i.e. close to 4°C). Such definitions were seen as ‘natural’, and certainly untainted by reference to any despised royalty, but problems (see metre; kilogram) led by 1799 to the creation of prototypes. Called the Mètre des Archives and the Kilogramme des Archives, the former became the defining entity, the latter merely a practical reference until 1872, but with what proved to be a small discrepancy of lasting impact; see litre; kilogram. (The ‘gramme’ has become the ‘gram’ very widely, the ‘metre’ and the ‘litre’ the ‘meter’ and ‘liter’ in US usage. The first of these changes is adopted in this publication but the others not, in deference to the more usual international practices.)

Rather than have independent names for the successive terms in any range of units, a range of standard decimal multiplier prefixes was introduced, with Greek terms for the integral multipliers and Latin for the fractional ones. By name and value significance, with etymological derivation and abbreviation, these were as shown in Table 33.

This has since been extended and varied, as shown under the SI system.

Table 33

Symbol	Prefix	Value	Etymology
m	milli-	10^-3	‘thousand’ in Latin
c	centi-	10^-2	‘hundred’ in Latin
d	deci-	10^-1	‘ten’ in Latin
D	deca-	10¹	‘ten’ in Greek
H	hecto-	10²	‘hundred’ in Greek
K	kilo-	10³	‘thousand’ in Greek
My	myria-	10⁴	‘ten thousand’ in Greek

It should be realized that this scheme of steps of ten, the literally decimal approach, was based on the idea that people did not use big integer values, as is common in North America, but always moved to larger units, as was characteristic in Europe. Thus, just as one would say 2 feet 8 inches in England and the equivalent elsewhere in Europe for what would usually be called 32 inches in America, the original metric terminology would have said, for a similar length, 8 decimetres 1 centimetre 2 millimetres rather than 812 mm or such. The decimal scheme, of course, meant no awkward conversions during additions, etc., as applied, for instance, when feet and inches were employed. But it facilitated just as readily, and more importantly, the discarding of the multi-unit expression in favour of the single-unit practice, particularly as the use of decimal fractions became more familiar. The current practice within metric of using a single unit has evolved over time as this fact climbed above ingrained habits, and as the populace became more arithmetically literate. (The easy North American practice of using single units with non-decimal British units, which largely obviates the consequences of them being non-decimal, is illustrated by measuring tapes of many feet in length but marked predominantly in inches, e.g. to 120 inches on a 10-foot tape. It is very conspicuous on freight vehicles, where the load limit is expressed in such style as 75 000 lb, when the British equivalent said 33 ton 9 cwt 2 qtr.)

Though the decimal steps within metric persist in everyday use in Europe and other traditional metric areas (even to such expressions as ‘a third of a decimetre’), North American metric practice largely abjures units other than the thousand multipliers, and indeed should be described as a millesimal scheme rather than a decimal one. The 13th CGPM in 1968 recommended that this practice should be general, at least in the sense that expressed powers of ten should have indices that are multiples of 3. While the SI has retained all the decimal prefixes from milli- to kilo-, it dropped the one decimal step beyond (the myria-) and, in expanding the range of prefixes, restricted them to millesimal steps. (Using only millesimal steps minimizes but does not remove the risk of misreading measurements on plans, for instance.)

The metre was a relatively large unit for common use, the gram a relatively small one; most market transactions would involve fractions of a metre but rarely be more precise than 10 grams, suggesting that the new scheme was rather ‘academic’, little orientated to the people at large, despite them being the essence of the recent revolution. The square metre was a reasonable unit of area, but the cubic metre extremely large for volume. Each could serve its respective dimension, along with the squares and cubes of the decimal multiples of the metre, but this would mean steps of 100 and 1 000 respectively in these compound dimensions for each decimal step in the linear. (For example, while 1 cm = 10 mm, 1 cm² = 100 mm² and 1 cm³ = 1 000 mm³.) To obviate this problem and make the system more acceptable to the public, the are for measuring area and the litre for volume were early additions to the system. Rather than being the obvious (and coherent) square and cubic metre, these introductions were set at one square decametre and one cubic decimetre, sizes more appropriate to their everyday jobs of measuring land and goods in the marketplace. (As discussed under litre, that unit, because of the manner of its definition, proved to be discrepant from the intended.)

A law of 1812 renewed in France the use of several old names but with metricized values, e.g. the toise of 2 metres, the pied of a third of a metre, the livre for half a kilogram. This accommodation of traditional terms was discontinued officially in 1840, but established a practice that continued in France and extended elsewhere.

Decimalization was also applied to time and to angles; the latter persisted as the grade, the former persisted only briefly, relative to the calendar and to the fractioning of the day.

Various derived terms combining the basic pair of metre and gram, plus the well-established second as the unit of time, were progressively introduced later, for scientific usage particularly. These included the dyne for a force of 1 centimetre·gram per second squared (= 1 cm·g·s^-2) and the erg for the energy of 1 dyne operating along 1 centimetre (1 cm²·g·s^-2). These, having their unit values involving the centimetre rather than the metre but otherwise the base units gram and second, were termed a c.g.s. system or scheme, which was termed ‘coherent’ because with such units all relationships involve only singular units. The British Association for the Advancement of Science extended this development to the electrical domain in the 1860s, based on defining a unit of electrical resistance, called the BA unit, in mechanical terms of the metre, gram, and second.
[Hartshorn L. Proc. Roy. Soc. London Ser. A Vol. 186, 185-91 (1946)] These, because of their reference back to non-electrical units, were called ‘absolute’ units. They were revised in the 1870s to have their unit coherence based on the centimetre rather than the metre, thus joining the dyne and other derived units within the c.g.s. scheme, forming the electromagnetic units. As discussed under that heading, these units were mostly far from the amounts to be measured, so decimally derived practical units, and subsequently slightly different international units, were adopted, before being replaced in 1948 with the current units which, in 1960, became part of the newly labelled SI system.

The use of the centimetre, along with the gram, in the various manifestations of the c.g.s. system illustrated the relative incompatibility of the metre and the gram. After early efforts with the natural combination of metre-gram-second, various other combinations were used to produce a convenient coherent system. Late in the 19th century Gauss used a millimetre-milligram-second system. At the other end of the scale, in 1919 France adopted an m.t.s. system based on the metre, tonne, and second. The modern vogue, and the structure of the SI, is the metre-kilogram-second combination. This m.k.s. system was adopted in 1946 as the primary international standard, effective for the beginning of 1948. The formal title Le Système International (the SI) was adopted in 1960. As this includes one electrical unit among its base units, chosen to be the ampere (the unit of current strength), the SI is classed as an m.k.s.A. system. (It has both the kelvin and the mole as physical base units too, plus the somewhat subjective candela.)

Britannica Concise Encyclopedia: metric system

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International decimal system of weights and measures, based on the metre (m) for length and the kilogram (kg) for mass, originally adopted in France in 1795. All other metric units were derived from the metre, including the gram (g) for weight (1 cc of water at its maximum density) and the litre (l, or L) for capacity (0.001 cu m). In the 20th century, the metric system became the basis for the International System of Units, which is now used officially almost worldwide.

For more information on metric system, visit Britannica.com.

Sports Science and Medicine: metric system

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A decimal system of measurements based on the metre which was intended to be 1/10 000 000 of a quadrant of the Earth through Paris. For scientific purposes, the metric system has been superseded by the SI system.

Columbia Encyclopedia: metric system

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metric system, system of weights and measures planned in France and adopted there in 1799; it has since been adopted by most of the technologically developed countries of the world. It is based on a unit of length, called the meter (m), and a unit of mass, called the kilogram (kg).

The system has changed somewhat since it was first developed; e.g., the definition of the meter has changed, and the unit for mass is different. The meter was originally intended to be ¹/_10,000,000 of the distance on the earth's surface between the equator and either pole; however, because of errors in the original survey for determining the meter and because of the impracticality of referring to such a standard, the meter was later redefined in terms of the standard prepared and kept at Sèvres, France, near Paris. Long defined as the distance between two scratches on a bar of platinum-iridium alloy, the meter in 1960 was first redefined in terms of an atomic standard. In 1983 the meter was officially redefined as the distance traveled by light in vacuum during ¹/_299,792,458 of a second.

The original unit of mass, the gram, was first defined as the mass of pure water at maximum density that would fill a cube whose edges are each 0.01 m. The unit of mass is now the kilogram, defined as the mass of a platinum-iridium cylinder kept at Sèvres. (A gram is now defined as a mass ¹/_1,000 kg.) Other metric units can be defined in terms of the meter and the kilogram. For example the are, the unit of area, is equal to the area of a square whose edges are each 10 m long. The liter, the metric unit of volume, is equal to the volume of a cube whose edges are each ¹/₁₀ m long.

Fractions and multiples of the metric units are related to each other by powers of 10, allowing conversion from one unit to a multiple of it simply by shifting a decimal point, and avoiding the lengthy arithmetical operations required by the English units of measurement. Standard prefixes (found in the table entitled Prefixes for Basic Metric Units) have been accepted for designating multiples and fractions of the meter, gram, are, and other units. Thus, 1,000 grams are a kilogram, 100 ares are a hectare, and ¹/₁₀₀ of a meter is a centimeter.

Several other systems of units based on the metric system have been in wide use. The cgs system is based on the centimeter of length, the gram of mass, and the second of time. The mks system is based on the meter of length, the kilogram of mass, and the second of time. Units in the mks system are larger than the corresponding cgs units. Electric and magnetic units have been defined for both of these systems; in fact, two different sets of electric units are defined in the cgs system. The mks system serves as the basis for the International System of Units, a comprehensive system of units for all physical quantities adopted in 1960 by the 11th General Conference on Weights and Measures.

Overview

One goal of the metric system is to have a single unit for any physical quantity; another important one is not needing 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 (kilometre), 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.

The original metric system was intended to be used with the time units of the French Republican Calendar, but these fell into disuse. Today decimal time is not in everyday use. Submultiples of the second (the microsecond for example) are used in scientific work but for lengths of time greater than a second traditional units, with their non-decimal conversion factors, are more often used than decimal multiples of the second. 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.

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 underway 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, that which is needed to incorporate the field of electromagnetism; As of 2006, this is the ampere, being the base unit of electrical 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 deca- (ten), hecto- (hundred), kilo- (thousand), mega- (million), and giga- (billion); deci- (tenth), centi- (hundredth), milli- (thousandth), micro- (millionth), and nano- (billionth). The most commonly used prefixes for multiples depend on the application and sometimes tradition. For example, long distances are stated in thousands of kilometres, not megametres.

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

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 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.^[10] 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. Clearly the advantages of decimal prefixes derive from our using base 10 arithmetic. 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.^[11] 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. The Greek prefix kilo~ and the Latin prefixes centi~ and milli~ are those most familiar from everyday use.

**metre**
Unit	Relation to base
megametre	10⁶ metres
kilometre	10³ metres
hectometre	10² metres
decametre	10¹ metres
decimetre	10⁻¹ metres
centimetre	10⁻² metres
millimetre	10⁻³ metres
micrometre	10⁻⁶ metres
nanometre	10⁻⁹ metres
picometre	10⁻¹² metres

**litre**
Unit	Relation to base
megalitre	10⁶ litres
kilolitre	10³ litres
hectolitre	10² litres
decalitre	10¹ litres
decilitre	10⁻¹ litres
centilitre	10⁻² litres
millilitre	10⁻³ litres
microlitre	10⁻⁶ litres

A similar application of Greek and Latin prefixes can be made with other metric measurements.

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 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,

1,000 litres = 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 multiple of 10. The standard acceleration due to gravity on Earth, g_n, 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, 299,792,458, has since become the definition.

A useful conversion used in meteorology is 1 m/s ≈ 2 knots, or actually 1.94384 knots (3% error,).^[12]

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 via the likes of Benjamin Franklin (who spent a great deal of time in London), and produced the by-product of the decimalised paper currency system, before finding favor with American revolutionary ally Louis XVI.^[13]

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 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.^[14] This also serves as the prototype in the SI. It included only few prefixes from milli (one thousandth) to myria (ten thousand).

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 measures usuelles. However, it is debatable^[who?] whether such systems are true metric systems.^{[clarification needed]}^{[citation 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.

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.

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 terminology

In keeping with American English spelling, meter, liter, etc. are used in the United States. 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.

Conversion and calculation errors

Cargo errors

The confusion between pounds (mass) and kilograms sometimes means that aircraft are overloaded. "the shipper's weights had been in kilograms, not pounds, and that, as a result, the aircraft was more than 30,000 pounds overweight".^[15]

Gimli Glider

In 1983 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. ^[16]

Mars Climate Orbiter

In 1999 NASA lost a $125 million Mars orbiter because one engineering team used metric units while another used US customary units for a calculation. ^[17]

Medical errors

Medical errors in the US are sometimes attributed to the confusion between grains and grams. A patient received phenobarbital 0.5 grams instead of 0.5 grains (0.03 grams) after the prescriber misread the prescription.^[18]

Notes and references

^ The World Factbook. (2006). Washington: Central Intelligence Agency. Retrieved 8 August 2006 from Appendix G.
^ http://metricationmatters.com/mm-newsletter-2003-07.html
^ http://science.jrank.org/pages/4291/Metric-System.html
^ http://www.cl.cam.ac.uk/~mgk25/metric-system-faq.txt
^ Letter from the UK Department for Transport, British Weights and Measures Association
^ HK Weights and Measures Ordinance
^ 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.
^ 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. Accessed 2007-08-03.
^ 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.
^ NTSB Order No. EA-4510, (1996), Washington, D.C.: National Transportation Safety Board, accessed August 3, 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 2007-08-21. "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. September 30, 1999. http://www.cnn.com/TECH/space/9909/30/mars.metric/. Retrieved 2007-08-21. "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."
^ ISMP Medication Safety Alert, (April–June 1999), Institute for Safe Medication Practices, accessed August 3, 2008.

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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

v • d • e Systems 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 · N-body

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Ancient systems	Greek · Roman · Egyptian · Hebrew · Arabic · Mesopotamian · Persian · Indian

Other systems	Non-standard · Mesures usuelles

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metric system

Contents

Overview

History

Replicable Prototypes

Decimal multiples

Prefixes

Practicality

Coincidental similarities

Metric systems

Original system

Centimetre-gram-second systems

Metre-kilogram-second systems

Metre-tonne-second systems

Gravitational systems

Variations in terminology

Conversion and calculation errors

See also

Multimedia

Notes and references