The metric system is a decimalised system of measurement. A system of measurment 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 It exists in several variations, with different choices of base 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 (SI) ("Système International d'Unités" in French, hence "SI") has been the internationally recognised standard metric system. French ( français,) is a Romance language spoken around the world by 118 million people as a native language and by about 180 to 260 million people A technical standard is an established norm or requirement It is usually a formal document that establishes uniform engineering or technical criteria methods processes and practices Metric units are widely used around the world for personal, commercial and scientific purposes. A standard set of prefixes in multiples of 10 may be used to derive larger and smaller units. However, the prefixes for multiples of 1000 are the most commonly used.

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. Liberia, officially the Republic of Liberia, is a country on the west coast of Africa, bordered by Sierra Leone, Guinea, Côte d'Ivoire Burma, officially the Union of Myanmar ( pjìdàunzṵ mjàmmà nàinŋàndɔ̀ is the largest country by geographical area in mainland Southeast Asia. The United States of America —commonly referred to as the

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 (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. Inches redirects here To see the Les Savy Fav album see Inches. A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit A yard (abbreviation yd) is a unit of Length in several different systems including English units Imperial units and United A fathom is a unit of Length in the Imperial system (and the derived U The rod is a unit of Length equal to 55 Yards 11 Cubits 50292 Meters 16 A chain is a unit of Length; it measures 66 feet or 22 yards (20 A furlong is a measure of Distance in Imperial units and US customary units. A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian. A league is a unit of Length or Area long common in Europe and Latin America, although no longer an official unit in any nation 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. In Mathematics, a fraction (from the Latin fractus, broken is a concept of a proportional relation between an object part and the object

The original metric system was intended to be used with the time units of the French Republican Calendar, but these fell into disuse. The French Republican Calendar or French Revolutionary Calendar was a Calendar proposed during the French Revolution, and used by the French government Today decimal time is not in everyday use. Decimal time is the representation of the Time of Day using units which are Decimally related 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. Louis XVI ( 23 August 1754 – 21 January 1793) Louis-Auguste de France, ruled as King of France and Navarre This article is about the country For a topic outline on this subject see List of basic France topics. 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. The grad is a unit of plane Angle, equivalent to of a full Circle, dividing a Right angle in 100 The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International For other uses of the words gram or gramme see Gram (disambiguation. The litre or liter (see spelling differences) is a unit of Volume. These were derived from each other via the properties of natural objects, mainly the Earth and water: 1 metre was originally defined as ¹⁄_40,000,000 of the polar circumference of the Earth, 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). EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Water is a common Chemical substance that is essential for the survival of all known forms of Life. The circumference is the distance around a closed Curve. Circumference is a kind of Perimeter. 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 Celsius Temperature scale was previously known as the centigrade scale. The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm

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 metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Iridium (ɪˈrɪdiəm is a Chemical element that has the symbol Ir and Atomic number 77 Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 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. For other uses of the words gram or gramme see Gram (disambiguation. 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. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units Solar times are measures of the apparent position of the Sun on the Celestial sphere. Varying choices have been made for the fourth base unit, that which is needed to incorporate the field of electromagnetics; As of 2006, this is the ampere, being the base unit of electrical current. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second Other quantities are derived from the base units; for example, the basic unit of speed is metres per second. Speed is the rate of motion, or equivalently the rate of change in position often expressed as Distance d traveled per unit of 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. 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 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. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The Celsius Temperature scale was previously known as the centigrade scale. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Absolute zero is the point at which molecules do not move (relative to the rest of the body more than they are required to by a quantum mechanical effect called Zero-point Zero degrees Celsius equals 273. 15 kelvins (the word "degree" is no longer to be used with kelvins since 1967-1968).

Angular measurements have been decimalised, but the older non-decimal units of angle are far more widely used. In Geometry and Trigonometry, an angle (in full plane angle) is the figure formed by two rays sharing a common Endpoint, called The decimal unit, which is not part of SI, is the gon or grad, equal to one hundredth of a right angle. In Geometry and Trigonometry, a right angle is an angle of 90 degrees corresponding to a quarter turn (that is a quarter of a full circle 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. Circles are simple Shapes of Euclidean geometry consisting of those points in a plane which are at a constant Distance, called the 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 scientific uses other than astronomy) or angular mils. The radian is a unit of plane Angle, equal to 180/ π degrees, or about 57 Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study An angular mil, also mil, is a unit of Angle. Origin of the name All versions of the angular mil are approximately the same size as a

History

Countries by date of metrication

In 1586, the Flemish mathematician Simon Stevin published a small pamphlet called De Thiende ("the tenth"). Metrication (or metrification refers to the introduction of the SI metric system as the International standard for physical measurements—a long-term series The terms Fleming and Flemings ( Vlaming and Vlamingen in Dutch) denote respectively a person and people and the Flemings or Simon Stevin (1548/49 &ndash 1620 was a Flemish Mathematician and Engineer. Decimal fractions had been employed for the extraction of square roots some five centuries before his time, but nobody established their daily use before Stevin. 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. John Wilkins ( January 1, 1614 - November 19, 1672) was an English clergyman and author The Royal Society of London for the Improvement of Natural Knowledge, known simply as The Royal Society, is a Learned society for science that was founded in 1660 ^[1] 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. Gabriel Mouton (1618 &ndash 28 September 1694) was a French abbot and scientist 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 Jean Picard as well as Huygens in 1673, and also studied at Royal Society in London. In 1673, 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 and was in a position 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 so instead of simply standardising size of the existing units, the leaders of the French revolutionary governments decided that a completely new system should be adopted.

The first official adoption of such a system occurred in France in 1791 after the French Revolution of 1789. This article is about the country For a topic outline on this subject see List of basic France topics. The French Revolution (1789–1799 was a period of political and social upheaval in the History of France, during which the French governmental structure previously an The creators of this metric system tried to choose units that were logical and practical. The revolution gave an opportunity for drastic change with an official ideology of "pure reason". It was proposed as a considerable improvement over the inconsistent collection of customary units that existed before, and that it be based on units of ten, because scientists, engineers, and bureaucrats at the time found this more convenient for the complex unit conversion they often must do.

The adoption of the metric system in France was slow, but its desirability as an international system was advocated by geodesists and others. Geodesy (dʒiːˈɒdɪsi also called geodetics, a branch of Earth sciences, is the scientific discipline that deals Since then a number of variations on the system evolved. Their use spread throughout the world, first to the non-English-speaking countries, and more recently to the English-speaking countries.

The whole system was derived from the properties of natural objects, namely the size of the Earth and the density of water, and simple relations in between one unit and the other. In order to determine as precisely as possible the size of the Earth, several teams were sent over several years to measure the length of as long a segment of a meridian as feasible. This article is about the geographical concept For other uses of the word see Meridian. It was decided to measure the meridian spanning Barcelona and Dunkirk which was the longest segment almost fully over land within French territory. This article is about the geographical concept For other uses of the word see Meridian. Barcelona ( Catalan bəɾsəˈlonə Spanish baɾθeˈlona is the capital and most populous city of the Autonomous Community of Catalonia Dunkirk ( French: Dunkerque, dœ̃kɛʀk or; Dutch:; is a harbour city and a commune in the northernmost part of France, in the It should be noted that even though, during the many years of the measurement, hostilities broke out between France and Spain, the development of such a standard was considered of such value that Spanish troops escorted the French team while in Spanish territory to ensure their safety. This article is about the country For a topic outline on this subject see List of basic France topics. Spain () or the Kingdom of Spain (Reino de España is a country located mostly in southwestern Europe on the Iberian Peninsula.

The whole process ended in the proclamation on June 22, 1799 of the metric system with the storage in the Archives of the Republic of the physical embodiments of the standard, the prototype metre and the prototype kilogram, both made in a platinum alloy, witnessed by representatives of the French and several foreign governments and most important natural philosophers of the time. Events 217 BC - Battle of Raphia: Ptolemy IV of Egypt defeats Antiochus III the Great of the Seleucid kingdom. Year 1799 ( MDCCXCIX) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a A scientist, in the broadest sense refers to any person that engages in a systematic activity to acquire Knowledge or an individual that engages in such practices The motto adopted for the metric system was: "for all men, for all time".

In revolutionary France the system was not particularly well accepted, and the old units, now illegal, remained in widespread use. On February 12, 1812, Napoleon, who had other concerns than enforcement of the system, authorised the usage of Mesures usuelles, traditional French measures redefined on the base of Metric System (toise as 2 metres, livre as 500 grams, etc. Events 1429 - English Forces under Sir John Fastolf defend a supply convoy carrying rations to the army besieging Orleans from attack by the Year 1812 ( MDCCCXII) a leap year started on Wednesday (link will display the full calendar of the Gregorian calendar (or a Leap year Mesures usuelles ( French for customary measurements) were a system of Measurement introduced to act as compromise between metric system and traditional ), and finally in 1816 a law made these Mesures usuelles standards. Mesures usuelles ( French for customary measurements) were a system of Measurement introduced to act as compromise between metric system and traditional This law was cancelled in 1825 and the metric system reinstated fully in 1837^[2]. It had already been reinstated in 1820 by a somewhat unlikely person, King William I of the neighbouring (United) Netherlands. William Frederick (William I, born Willem Frederik Prins van Oranje-Nassau ( The Hague, 24 August 1772 - Berlin, 12 December 1843 was a Prince of Although he was generally considered more conservative, he was desperate to bring at least some form of unity to his rather disunited kingdom and stimulate the industrial development of the South. Although the imposed system was metric, a number of old local names like 'pond' (pound) and 'ons' (ounce) were substituted for 500 g and 100 g respectively, and although they were officially abolished in the 1870s, they survive to the present day. The king's attempts were in vain in that Belgium claimed its independence from the Netherlands, but the metric system survived and began a slow but steady conquest of the world. By the 1960s, the majority of nations were on the metric system and most that were not had started programmes to fully convert to the metric system (metrication). Metrication (or metrification refers to the introduction of the SI metric system as the International standard for physical measurements—a long-term series As of 2007 only three countries, the United States, Liberia, and Myanmar (Burma) had not mandated the metric system upon their populace. The United States of America —commonly referred to as the Liberia, officially the Republic of Liberia, is a country on the west coast of Africa, bordered by Sierra Leone, Guinea, Côte d'Ivoire Burma, officially the Union of Myanmar ( pjìdàunzṵ mjàmmà nàinŋàndɔ̀ is the largest country by geographical area in mainland Southeast Asia.

Later improvements in the measurement of both the size of the Earth and the properties of water revealed discrepancies between the metric standards and their originally intended values. The Industrial Revolution was well under way and the standardisation of mechanical parts, mainly bolts and nuts, was of great importance and they relied on precise measurements. The Industrial Revolution was a period in the late 18th and early 19th centuries when major changes in agriculture manufacturing and transportation had a profound effect on the Though these discrepancies would be mostly hidden in the manufacturing tolerances of those days, changing the prototypes to conform to the new and more precise measurements would have been impractical particularly since new and improved instruments would continually change them.

It was decided to break the linkage between the prototypes and the natural properties they were derived from. The prototypes then became the basis of the system. The use of prototypes, however, is problematic for a number of reasons. There is the potential for loss, damage or destruction. There is also the problem of variance of the standard with the changes that any artifact can be expected to go through, though they be slight. Also whilst there may be copies, there must be only one official prototype which cannot be universally accessible.

The metre had been defined in terms of such a prototype and remained so until 1960. At that time, the metre was defined as a certain number of wavelengths of a particular frequency of light emitted by a certain element. Since 1983 the metre has been defined as the distance light travels in a given fraction of a second in a vacuum. Thus the definition of the metre ultimately regained a linkage with a natural property, this time a property thought immutable in our universe and truly universal. The kilogram is now the only base unit still defined in terms of a prototype. Since 1899, the kilogram has been formally anchored to a single platinum-iridium cylinder in Sèvres, France.

On May 20, 1875 an international treaty known as the Convention du Mètre (Metre Convention) was signed by 17 states (including France, Germany, Norway, Russia, Spain, Sweden, Switzerland, etcetra). Events 325 - The First Council of Nicaea &ndash the first Ecumenical Council of the Christian Church is held Year 1875 ( MDCCCLXXV) was a Common year starting on Friday (link will display the full calendar of the Gregorian calendar (or a Common The Convention du Mètre of May 20, 1875 is an international treaty that established three organizations to oversee the keeping of metric standards This treaty established the following organisations to conduct international activities relating to a uniform system for measurements:

1. Conférence générale des poids et mesures (CGPM), an intergovernmental conference of official delegates of member nations and the supreme authority for all actions;
2. 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;
3. 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. 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 The International Bureau of Weights and Measures ( Bureau international des poids et mesures, in French) is an international Standards organization, one

The metric system is used widely for scientific purposes but there are some exceptions, especially at large and small scales, such as the parsec. History The first direct measurements of an object at interstellar distances were undertaken by German Astronomer Friedrich Wilhelm Bessel in 1838 It has been adopted for everyday life by most nations through a process called metrication. Metrication (or metrification refers to the introduction of the SI metric system as the International standard for physical measurements—a long-term series As of 2006, 95% of the world's population live in metricated countries, although non-metric units are still used for some purposes in some countries. The holdouts to full metrication are the United States and, to a lesser degree, the United Kingdom, where there is public attachment to the traditional units. The United States of America —commonly referred to as the The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located

Goals

The metric system was designed with several goals in mind.

Neutral and universal

The designers of the metric system meant to make it as neutral as possible so that it could be adopted universally.

Replicable

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.

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. This article is about the geographical concept For other uses of the word see Meridian. They discarded the use of a pendulum since its period or, inversely, the length of the string holding the bob for the same period changes around the Earth. A pendulum is a mass that is attached to a pivot from which it can swing freely 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.

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 (e. g. 29/64) 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. The decimal ( base ten or occasionally denary) Numeral system has ten as its base. 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. 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 Thus the prefix kilo could be used both 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 while a quintal is accepted as 100 kilograms; both are derived from old customary units and were rounded to metric. This article is about the tonne or metric ton For other tons see Ton. The quintal or centner is a historical unit of Mass with many different definitions in different countries but usually it is 100 base units of mass e

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. ^[3] If the prefix is Greek-derived, the measure is multiplied by this factor. If the prefix is Latin-derived, it is divided. The Greek prefix kilo~ and the Latin prefixes centi~ and milli~ are those most familiar from everyday use.

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

Relation of volume and mass of water

Originally, units for volume and mass were directly related to each, with mass defined in terms of a volume of water. Water is a common Chemical substance that is essential for the survival of all known forms of Life. 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.

Practical

The base units were chosen to be of similar magnitude to customary units. 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. A toise (symbol T) is a unit of measure for Length, Area and Volume originating in pre-revolutionary France 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. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the

Coincidental similarities to real-life values

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, which is the value at about 45° north or south of the equator. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units Accordingly the force exerted on a mass of one kilogram in Earth gravity (F = m·a) is about ten newtons (kg-m/s²). In Physics, a force is whatever can cause an object with Mass to Accelerate. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object This simplified the metrication of many machines such as locomotives, which were simply re-labelled from e. g. "85 tonnes" to "850 kN". This article is about the tonne or metric ton For other tons see Ton. A closer approximation is π² m/s², which means a one-metre pendulum has a period of almost exactly two seconds. A pendulum is a mass that is attached to a pivot from which it can swing freely

Also, the standard atmospheric pressure, previously expressed in atmospheres, when given in pascals, is 101. The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm 325 kPa. Since the difference between 10 atmospheres and 1 MPa is only 1. 3%, many devices were simply re-labeled 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 turns out to be astonishingly close (0. 07% error) to 3×10⁸ m/s.

A useful conversion used in meteorology is 1 m/s ≈ 2 knots with less than a 3% error, actually 1. 94384 knots (to 5 decimal places). The equivalent conversion for distance is not so "rounded", 1 nautical mile = 1. A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian. 852 km (exactly) = 1 minute of arc Latitude (approximately). Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the ^[4]

Metric systems

Original system

The metric system, and 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 favour with American revolutionary ally Louis XV. ^[5]

The original French system continued the tradition of having separate base units for geometrically related dimensions, i. e. metre for lengths, are (100 m²) for areas, stere (1 m³) for dry capacities and litre (1 dm³) for liquid capacities. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Conversions One are is equivalent to Metric 00001 km2 (square kilometres 0 The stère is a measurement unit for Volume of wood and equals one Cubic metre. The litre or liter (see spelling differences) is a unit of Volume. The hectare, equal to a hundred ares, is the area of a square 100 metres on a side (about 2. Explanation The hectare is commonly used in most countries around the world especially in domains concerned with land planning and management such as Agriculture, Conversions One are is equivalent to Metric 00001 km2 (square kilometres 0 5 acres), and is still in use to measure fields. The acre is a unit of Area in a number of different systems including the imperial and U

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 "gramme" 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. ^[6] This also serves as the prototype in the SI. It included only few prefixes from milli, one thousandth to myria ten thousand. 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 "Milli" redirects here for the village in Azerbaijan see Birinci Milli; for similar-sounding words see Millie.

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. The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass An example of these is mesures usuelles. Mesures usuelles ( French for customary measurements) were a system of Measurement introduced to act as compromise between metric system and traditional However it is debatable whether such systems are true metric systems.

Centimetre-gram-second systems

Early on in the history of the metric system various centimetre gram second systems of units (CGS) had been in use. The centimetre-gram-second system ( CGS) is a system of physical units. These units were particularly convenient in science and technology. For example, in CGS the density of water is approximately 1 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. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units Metre-kilogram-second-coulomb (MKSC) and metre-kilogram-second-ampere (MKSA) systems are extensions of these. The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second

The International System of Units (Système international d'unités 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. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The candela (kanˈdɛlə /-ˈdiːlə/ symbol cd) is the SI base unit of Luminous intensity; that is power emitted by a light source in a particular The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this

Metre-tonne-second systems

The metre-tonne-second system of units (MTS) was based on the metre, tonne and second. The metre-tonne-second or mts system of units is a system of Physical units It was invented in France hence the unit names sthène and pièze This article is about the tonne or metric ton For other tons see Ton. It was invented in France and mostly used in the Soviet Union from 1933 to 1955. The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991

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. In the gravitational metric system(s the base unit of force is not normalised to one mass unit ( Gram or Kilogram) times one length unit ( Metre or centimetre The unit kilogram-force ( kgf, often incorrectly just kg) or kilopond ( kp) is defined as the Force exerted by Earth's gravity In the gravitational metric system(s the base unit of force is not normalised to one mass unit ( Gram or Kilogram) times one length unit ( Metre or centimetre The slug is an English unit of Mass. It is a mass that accelerates by 1 ft/s² when a force of one Pound-force (lbf is exerted on it Note these are not part of the International System of Units (SI).

Variations in terminology

In keeping with American English spelling, meter, liter, etc. American and British English spelling differences are one aspect of American and British English differences. are used in the United States. In addition, the official US spelling for the rarely used SI prefix for ten is deka. deca- or deka- is an SI prefix (symbol da) in the SI system of units also a Numerical prefix (from Greek δέκα 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; 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

• Gimli Glider — In 1983 a Boeing 767 jet ran out of fuel in midflight because of two mistakes in figuring the fuel supply of Air Canada's first aircraft to use metric measurements. Gimli Glider is the nickname of an Air Canada aircraft which was involved in an infamous Aviation incident Air Canada () is Canada 's largest Airline and Flag carrier. The airline founded in 1937 has had its corporate headquarters in Montreal ^[7]
• 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. The Mars Climate Orbiter (formerly the Mars Surveyor '98 Orbiter was one of two spacecraft in the Mars Surveyor '98 program, the other being the Mars Polar Lander ^[8]

Notes and references

See also