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Metrication, or metrification, is the process of converting from the various other systems of units used throughout the world (especially the "Imperial" or "American" systems, originating in the United Kingdom) to the metric or SI (Système International) system.
All countries in the world use the metric or SI systems to a greater or lesser extent, and most have abolished the use of non-metric units for almost all purposes; a notable exception is the various non-SI units related to sea and air transport (as specified below).
The United States, Liberia, and Myanmar have not "officially" adopted everyday use of the metric system. Despite the lack of "official" adoption of the metric system in Liberia and Myanmar, unofficial metrication has taken place there, and the economies of these two countries do primarily operate using the metric system. Additionally, the United States Military makes extensive use of the metric system in its operations. SI units are commonly used in many scientific and engineering areas. The dual use of systems other than SI is common in certain areas. In the UK, for example, speed limit signs are still posted in miles per hour and other transitional or colloquial circumstances exist throughout the world.
The modern SI is based on the older MKS (Mètre-Kilogramme-Seconde) division of metric measurements, but with addition of the kelvin (temperature), candela (luminous intensity), mole (amount of substance) and ampere (electrical current), bringing the number of base units to seven. For a while there was heated contention with the CGS (Centimetre-Gram-Second) and some areas of science still use this form of the system, even though it is not the international standard any more. No metre-gram-second configuration was ever used which eliminated the prefixes entirely. There are a great number of derived units in both systems, and there is difficulty moving between branches of the Metric System on some of these units. Some obsolete metric units such as the micron, the mho, the calorie and the Ångström have proved difficult to eradicate.
The base unit of time in the modernized metric system is the second. The minute, hour and day are officially "non-SI units accepted for use with the International System", even though for strict scientific use standards agencies recommend only the second and metric multiples and submultiples of the second. So for example, kilometres per hour (km/h) is an accepted unit of speed in the metric system, but metres per second (m/s) would be preferred in a scientific setting.
The original metric system did not include a metric time unit. Although decimal time was introduced in France after the French Revolution as part of the French Republican Calendar, it was not related to the metric system and was abandoned after two years for lack of public support, at the same time the metric system was introduced. Carl Friedrich Gauss advocated the addition of the second, defined as 1/86400 of a mean solar day, as a metric unit in 1832, which was later incorporated as a fundamental unit of both the CGS and MKS metric systems. The SI second has been redefined in terms of the vibrations of atoms for greater precision, since the exact length of the day varies slightly with the rotation of the earth. Civil time in most countries is standard time, defined by offsets from Coordinated Universal Time, which is a time scale that is based upon a count of an integral number of SI seconds.
Air and sea transport
As stated, non-metric measures in air and sea transport retain worldwide dominance. In these areas the nautical mile (1.852 km) is preferred over the kilometre, because it closely represents a minute of arc of the circumference of Earth. While the metre was also based on the Earth with 100 km equal to an arc of 1 gon, those units of angle have not seen widespread use, though they do appear on some maps. The gon is a recent name for what is still also called a grad or grade; thus kilometre : centigrade : : nautical mile : minute of arc.
The knot, which is nautical miles per hour, remains the prime unit of speed for maritime and air navigation (although before the 1960s, statute miles per hour—which bear no relationship to the Earth—were most often used for this purpose, and they remained in fairly common use for some purposes into the 1970s and later). For aircraft flying, altitudes are in most places calculated from air pressure to feet (in steps of 100) rather than metres. Since aircraft pilots and air traffic controllers have long been trained to use non-metric units, the potential threat to air traffic safety has been cited as a reason for not adopting metric measurement in this area. Helicopter pilots and many Eastern European air forces (mainly, but not only former Warsaw Pact) are using metres, however.
Process of conversion
There are three possible major steps in converting from traditional measurements to metric:
- Allow the use of metric units,
- parallel with traditional ones,
- base the definitions of traditional units upon their metric counterparts,
- make these redefinitions round metric values,
- decimalize the factors between traditional units,
- enforce metric units and disallow traditional ones.
Not all of these steps are necessary or advisable, but most have been taken by all countries over the past two centuries. For example, many local pounds have had been redefined to be 500 g exactly and are informally used to present day—the English ones (Avoirdupois and Troy) have not. The mere decimalization of old units, e.g. 10 inches to the foot (Sweden etc.), has been unsuccessful in most cases: people just fully converted to metric instead.
Metrication generally requires legislative action to overcome resistance and inertia among populations familiar with another system, i.e. legal requirements to use metric units in commerce, and the eventual prohibition of the use of non-metric units. Without such legislation businesses may not want to convert to metric standards, because of the habitual preference of consumers for the familiar. Those countries that have attempted to engineer a voluntary conversion to the metric system, such as the United States, have been largely unsuccessful. Countries that forced the change by making the metric system legally compulsory have been more successful.
With the ever-increasing importance of global trade, increasing harmonization of units of measurement and standards has taken place. This does not necessarily have to mean metrication: many Canadian and Mexican companies cannot fully metricate or even have to step back to using Imperial units because of the importance of the US market to their export trade.
Often, but not necessarily, metrication involves redesigning standards to use smooth metric sizes. For example, 1 inch is a rational size for a bolt if the bolt is to be measured in inches, but the metric equivalent of 25.4 mm is not only not a rational size but does not even exist, and thus the metric size of M24 might be substituted. This requires not only selecting a different type of the bolt, but also a redesign of many other products and structures that would contain the bolt. In many other cases there is little difficulty, though.
It is often claimed that the changeover to common metric sizes by businesses and manufacturers is used as an opportunity to raise the price for a given amount of product, taking advantage of consumers' unfamiliarity with a new size, but there have been a number of examples of the contrary (e.g. 2-litre Coca-Cola bottle). A common reason for continuing to display unit prices "per pound" as opposed to "per kilogram" is that the price appears half as much.
A single failure to convert between units was the contributing factor in the loss of the Mars Climate Orbiter in its crash on Mars. The manufacturer of the spacecraft had designed the navigation system to be programmed in Imperial measurements, whereas the navigation team at NASA's Jet Propulsion Laboratory in Pasadena, California controlled the spacecraft using metric units.
Metrication around the world
The main exception to standardized metrication is the United States. Although metrication is the official policy of the American government since the Metre Convention, and several laws encourage or require use of metric units in various contexts , the progress of metrication has been much slower in the United States than in the rest of the world. Non-metric units continue to be predominantly used in everyday life, and in commerce, engineering, and aviation. However, change has occurred, with most products within the U.S. now required by law to be labeled with both metric and non-metric units, and a number of companies and government agencies switching to metric standards.
One peculiar example of this is bottled soft drinks, commonly sold in units of two litres with units of one and three being less common. This is a result of the introduction of PET bottling technology coinciding with a particularly strong metrication push in the late 1970s; consumers found that they could buy a two-litre plastic bottle of their favorite soft drink more cheaply than they could four one-pint glass bottles, and the convention stuck. Smaller units, however, continue to be sold in fluid ounces, as with 8-ounce (240 ml) and 12-ounce (355 ml) aluminum cans and 20-ounce (591 ml or 600 ml) PET bottles.
The United States continues to use only miles for road distance signs, with the exception of Interstate 19 in Arizona. Originally U.S. legislation set October 2000 as a deadline by which states must undertake construction work and statistics in metric for states to be eligible for federal funding, but that requirement has since been rescinded. Some states, such as California, have experimented with metric road signs, but there are as yet no plans for large-scale conversion. There is presently little political support for a comprehensive switch to the metric system.
Metric units are generally used in military and scientific applications in the USA with some exceptions like BTUs.
Metrication of property title in the United States is not likely in the foreseeable future. Land titles in most of the country are tied to the Public Land Survey System, which was largely completed before the mile was redefined in terms of the metric system. In the creation and definition of survey townships, PLSS uses statute miles, which differ from metric-referenced miles by a few millimetres.
Europe generally uses metric units for almost all purposes, and uses metric standards. Some non-metric units are still popularly used in some countries, including the pint and mile in the UK. In other cases, the term for a traditional measure has been affixed to a metric one. For instance, the Continental "metric pound" (German Pfund, French livre, or Dutch pond) is popularly defined as 500 grams. Similarly, the "metric ounce" (Dutch ons) is defined as 100 grams.
Metrication was first begun in France during the French Revolution, although some of these revolutionary efforts were abandoned. The metrication of units of time was originally a part of the plan, but this failed to receive popular support. By about 1900, metrication had spread over much of continental Europe.
The Republic of Ireland has now completed the changeover process. Metric speed limits came into force nationwide on 20 January 2005, and while the huge majority of road distance signs in the country are in kilometres the remaining few (mostly on low-volume rural roads) have a deadline, by which they all must be changed of 1 January 2006 (although they have probably nearly all been changed at this point). Also, for educational purposes, for at least 20 years only metric units have been taught, as they are the sole system used for state exams. All government departements are required to use the metric system.
However, one main exception in the Republic of Ireland is the pint which is used mainly as alias for "glass of beer", but this should not be confused with the situation in the UK, where it is illegal to sell beer in litres, as this is perfectly legal. It is in fact illegal to BY pints (i.e. you can sell drinks in pints, but can't charge per pint, for example you can sell beer at €5 for a pint glass of beer, but can't sell it at €5/pint, which is the case in the rest of Europe, except of course the UK). GoMetric.ie
The United Kingdom is the main exception; this country is in the process of phasing out the legal status of most non-metric units. Thus it uses a mix of metric and non-metric units for different purposes. The United Kingdom is currently in the process of abolishing the use of most non-metric units; as of 2000, all loose goods sold by reference to units of quantity had to be sold using metric units. UK policy is to eliminate by 2009 almost all non-metric units when used for goods and services sold by quantity. Goods and services sold by a description are not covered by weights and measures legislation. Thus, a fence panel sold as "6 foot by 6 foot" will continue to be legal after 2009 but a pole sold as "50 pence per linear foot" is illegal. Road signs will, however, remain non-metric. The only non-metric units allowed for trade of goods and services sold by quantity after 2000 are:
- The mile, yard, foot and inch for road signs and related uses,
- the acre for land registration,
- the troy ounce for trading in precious metals,
- the foot for aircraft altitudes,
- the nautical mile and knots for sea and air traffic and meteorology,
- the pint for draught beer, cider and milk when sold in returnable containers.
Draught beer and cider are the only goods that may not be sold in metric units in the United Kingdom; the only legal measures for these drinks when sold on draught are ⅓ pint (190 ml) (rarely encountered), ½ pint (284 ml) and integer multiples of the latter.
The use of metric units has been legal in the UK for all purposes since 1897. The idea was first discussed by a Royal Commission that reported in 1818 . In 1862, the Select Committee on Weights and Measures favoured the introduction of decimalisation to accompany the introduction of metric weights and measures . A further Royal Commission "on the on the question of the introduction of metric system of weights and measures" also reported in 1869 .
Despite the slow progress of metrication, its sole adoption was first recommended by the Committee on Weights and Measures (Hodgson Committee) in 1950, and accepted by the President of the Board of Trade in May 1965. As a result, metric units have been taught in UK schools since the late 1960s, and certain industries also converted or largely converted decades ago. For example the paper industry converted in 1970, and the construction industry between 1969 and 1972—although certain products continue to be produced to imperial sizes but with metric size descriptions, for example as 13 mm (rather than as half-inch) thick plasterboard.
Canada has converted to the metric system for most purposes, including temperature in weather reports, speed limits, road signs, and sizes of most products. However there is still significant use of non-metric units and standards in some sectors of the Canadian economy, mainly due to the close proximity to the United States. Notable among these are stationery, construction lumber, and drywall—retrofitting metric-sized (designed for 400 mm centres) wallboard on old 16" (406.4 mm) spaced studs can be significantly difficult.
Since metrication was an artificial process initiated by the government, Canadians who were born before the 1970's still use English units for common informal measurements. A person's height and weight are normally calculated using the traditional English or U.S. units and descriptions of criminal suspects are still often publicized in this way - foot and pound, while area (for reasonably small areas such as floorspace) is measured in square feet. Fahrenheit is used for cooking as are U.S. cooking measurements although appliances are usually labelled with degrees Celsius as well. Although the media is required to report weather in metric, older Canadians still "feel" the temperatures more subjectively in degrees Fahrenheit.
Grocery stores advertise most products sold by weight in both price per pound and per kilogram but the pound price is prominent mainly because the price per pound appears cheaper than the price per kilogram. The biggest exception is deli items that are sold (and advertised) per 100 g. Since the price per 100 g appears cheaper than the price per pound, it is usually the only price listed. Most Canadians order their deli items in metric quantities.
Fast-food restaurants often advertise measurements of food and drink in imperial units, either because the containers are made to U.S. standards, or the franchise is U.S. based and uses a standard size for its products, or to make it more difficult for consumers to compare prices between the restaurant's products and those of grocery stores.
Australia, New Zealand and South Africa
Australia and New Zealand have largely been converted to the metric system since the 1970s, but non-metric units are still sometimes used in popular conversation, especially to measure body height—some Australians know their height in feet and inches but their mass in kilograms. This is changing, however, as most people born after 1980 use the metric system only. In South Africa, where the conversion to metric was completed in 1978, non-metric measurements are rarely encountered in popular conversation, and use of the decimal comma (used in European languages) is often encountered in South African English, instead of the decimal point, as is the case elsewhere in the English-speaking world.
In Australia, a metrication board was created in 1966 and dissolved in 1981 once the conversion to metric was completed. During this time, a Metric Conversion Act was passed. For additional background, see the report Metrication in Australia by Kevin Joseph Wilks (DITAC - Department of Industry, Technology and Commerce).
Use of metric or metrified traditional units is general. In informal situations, weights are typically given in metric jin (500 grams), heights of persons in metres, distances in metric li (500 metres).
The anti-metrication movement
Anti-metrication (or anti-metrification) is rejection of metrication in favor of a different system of measurement, typically the American or the different Imperial one. Such efforts to prevent metrication have largely failed, except in the United States.
Some opponents of metrication have become known colloquially in the UK as "metric martyrs" (the term is used by both supporters and opponents of metrication).
The basic philosophy of anti-metrication is that non-metric systems of measurement were developed organically from actual use (thus units which share names with physical objects, such as the foot, hand, barrel, cord) and are therefore properly suited for normal usage, whereas the metric system is based on easy decimal conversion between various units, not natural usage.
|Divisor||Imperial (base 8)||Metric (base 10)||Imperial (base 12)||Imperial (base 16)|
A commonly quoted reason for preferring non-metric units is the ease with which they can be divided by common fractions. For example, dividing by three is simple in a base-12 system, but difficult with a base ten. Even taking a quarter in base ten gives a fraction, whereas in many non-metric systems this too is easy. However, only few parts of the U.S. customary system actually feature the factor twelve, namely the inch-to-foot ratio and the troy-ounce-to-pound ratio. Powers of two are more common, especially in volume measures, along with other factors (5, 7, 11).
Metric practitioners counter to such arguments that they have a much better solution. Although, the SI standard itself defines no preferred sizes, there exist several widely used guidelines tailored to the needs of particular fields. For example, in the construction industry, a system known as modular coordination is commonly used. It prefers major dimensions that are multiples of 300 mm or 600 mm, leading to component sizes such as 1200 mm × 2400 mm. Any multiple of 600 mm can be divided by 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 25, 30 far more easily than this is the case with US customary measures, without any need for fractions. Other such guidelines for preferred numbers include the Renard series or the system of metric paper sizes.
Another commonly quoted reason against metrication is the difficulties that conversion to and from old units cause. For everyday usage a 500-g pound, 4-l gallon and 25-mm inch could suffice, and have been used.
For some, anti-metrication is a form of traditionalism, looking to a history of usage that stretches back centuries or even millennia. Sometimes it is even considered part of patriotism. For traditional argument, however, the US system is based upon the English system, which in turn has largely Roman and French (i.e. Avoirdupois) roots.
The non-metric units have changed meanings many times throughout history. At the time of the French revolution there were over 5000 variations on the foot alone. Which one would be traditionally correct? The so-called Imperial system is the result of a clean-up in 1824, some 30 years after the founding of the metric system. Even in those days there was resistance to Imperial from users of the abolished older units.
Metric units, however, have not been exempt from redefinitions or refinements. The metre, for instance, was intended to equal 10−7 or one ten-millionth of the length of the meridian through Paris from pole to the equator. However, the first prototype was short by 0.2 millimetres because researchers miscalculated the flattening of Earth due to its rotation. Now it is the length travelled by light in vacuum during the time interval of 1/299 792 458 of a second.
Another complaint regarding SI is the alleged unpleasantness of its terms. Supporters of other systems claim that, being designed for scientific use, most metric terms are "cold", "harsh" and lack the character of their Imperial counterparts.
For example, most common Imperial measurements, except 'gallon', are single-syllable ('inch', 'foot', 'yard', 'mile', 'ounce', 'pound', 'ton', 'cup', 'pint', 'quart') which would be more "appealing" to the tongue and ear than "lifeless" terms like 'decimetre' or 'millilitre'. In English, the names of the metric units, with their prefixes of multiple origins, are imperfectly domesticated loanwords. The corresponding traditional units, though not all of Anglo-Saxon etymology, have been in use long enough to conform thoroughly to regular English phonology. The irregular correspondence between spelling and pronunciation of a foreign word like litre, by contrast, marks it as an intruder.
While there are those who claim this objection is mere parochialism , its existence can be helpful in understanding how much people "hold dear" the units they grew up with, and the difficulties encountered in the metrication process. Even in countries that have gone metric, the Imperial terms continue to be used metaphorically and in fixed expressions. Those opposed to metrication will not be forced to say "a gram of prevention is worth a kilogram of cure" or "I was a million kilometres away (in my thoughts)" or "Due to the heavy traffic jam, the cars just centimetreed their way down the road".
Another basic argument is that the adoption of metric units has almost always been a matter of government compulsion, prohibiting people from using units they were used to, and that such policies are wrong in principle. The idea of compulsory standards is hardly new, however; in the mid-1820s, the Act for ascertaining and establishing Uniformity of Weights and Measures, signed by George IV, consolidated the various gallons in use at the time and established a new Imperial gallon, simultaneously prohibiting the use of the older units. In the UK there is widespread non-compliance by small-scale fruit and vegetable traders with the requirement to price in metric. Display of "supplementary units" (the equivalent Imperial price) is permitted (until 31st December 2009) as long as they are no larger than, nor more prominent than, the legally-binding metric price. In many towns, fruit and veg markets display prominent signs in Imperial units, with a very small metric price beside them. There is also some degree of non-compliance by smaller vendors of carpets, despite the great simplication that metrication affords to carpet-buying. Large supermarkets in the UK have also attempted to undermine the metrication process. They place small metric price signs on the edges of shelves and use these to claim they are pricing in metric. However, all around the store are very large signs advertising the products purely in Imperial units. They claim that the law requires them to price in metric but does not require them to advertise in metric. So far, Trading Standards officers have not taken a supermarket to court over this issue and thus its legality remains untested.
Anti-metrication in the UK often manifests itself in conjunction with Euroscepticism because of the belief that the European Union is responsible for compulsory metrication, although metrication had been government policy since 1953 and the process was initiated by the government establishing the Metrication Board in 1969, four years before joining the EC. In more recent times, anti-metrication supporters have claimed that the legal compulsion to adopt the metric system instead of their traditional weights and measures is an infringement of their human rights to freedom of speech, though this claim has been consistently rejected by the courts. Most recently, on 25 February 2004, the European Court of Human Rights rejected an application from British shopkeepers refusing to use metric claiming that their human rights had been violated.
Ideology of the metric system
The metric system was invented by French scientists, and was proposed for widespread non-scientific use as a result of the French Revolution of 1789. The metric system was designed as part and parcel of the revolution's official ideology of "Pure Reason".
At the same time the metric system sought to impose "Pure Reason" on weights and measures, the French revolutionary calendar was also devised; this calendar was designed as an explicit attack on the Christian year, replacing the week with decades of ten days, thereby removing the sabbath or the Lord's Day as a regular part of the calendar. In addition to the new calendar, these attempted reforms also included metric time, dividing the day into 10 "hours" with 100 "minutes".
Napoleon Bonaparte abolished the metric calendar to meet the objections of the Roman Catholic Church in 1806. Decimal time died of neglect well before that, while other measurements (gram, litre, metre) persisted. It has been argued that the metric system suffers from monomaniacal decimalism, i.e. a "tunnel visioned" insistence on ten as the sole multiplier or divisor among permitted units, and thereby sacrifices convenience and human scale for the sake of mathematics.
In the United States, a large nation that shares borders with only two other countries (Canada and Mexico), residents tend not to leave the country very often as going anywhere but the two border states is quite expensive, and consequently the wave of metrication elsewhere in the world has not made much of an impact. Many Americans see little practical benefit in making a complete switch to the metric system and note that doing so would bring a considerable cost to taxpayers. Most U.S. citizens are more or less content with their present status and feel that their country has more pressing needs at hand than changing measurement systems.
Related international standards
Although the metric system is for specifying products and their components only, lumped in with the notion of metrication is often the acceptance of a whole set of international standards:
- Sizes of standard paper, the reams in which they are packed, the locations of holes for ring binders, and the boxes and filing cabinets which contain them;
- though the geographic measurements on maps are of course in metres and kilometres, the scales of the maps themselves are limited to a few standard ones;
- bed frames, mattresses, and their sheets;
- not only the trivial grocery changes of butcher's meat scales and the change of liquor from a fifth of a gallon to 750 millilitres (which sometimes resulted in similar changes in the metric world, such as a change of German wine bottles from 700 ml to 750 ml), but also the entire range of cans for preserving foods.
These are what international organizations have specified and have been taken up in fully metric countries. Only the sizes of shoes and clothing are usually multiply labelled.
- conversion of units
- Metric clothes sizes
- Preferred numbers
- US Metric Association
- Metric Martyrs
- The Metrication Board of Ireland
- the United Kingdom Metric Association campaigns for a total metric switchover in the UK
- U.S. Metric Association discusses progress of metrication in several countries. By country, direct to portion of the page:
- Freedom to Measure discusses the freedom to choose a measurement system
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