Editing Metrication (section)

==Methods of conversion==
There are three common ways that nations convert from traditional measurement systems to the metric system. The first is the quick or "Big-Bang" route. The second way is to phase in units over time and progressively outlaw traditional units. This method, favoured by some [[industrial nation]]s, is slower and generally less complete. The third way is to redefine traditional units in metric terms. This has been used successfully where traditional units were ill-defined and had regional variations.

The "Big-Bang" way is to simultaneously outlaw the use of [[history of measurement|pre-metric]] measurement, metricate, reissue all government publications and laws, and change education systems to metric.  [[India]] was the first Commonwealth country to use this method of conversion. Its changeover lasted from 1 April 1960, when metric measurements became legal, to 1 April 1962, when all other systems were banned. The Indian model was extremely successful and was copied over much of the developing world.  Two industrialized Commonwealth countries, Australia and [[New Zealand]], also did a quick conversion to metric.

The phase-in way is to pass a law permitting the use of metric units in parallel with traditional ones, followed by education of metric units, then progressively ban the use of the older measures.  This has generally been a slow route to metric.  The [[British Empire]] permitted the use of metric measures in 1873, but the changeover was not completed in most Commonwealth countries other than India and Australia until the 1970s and 1980s when governments took an active role in metric conversion.  In the United Kingdom and Canada, the process is still incomplete.  Japan also followed this route and did not complete the changeover for 70&nbsp;years.  By law, loose goods sold with reference to units of quantity have to be weighed and sold using the metric system.  In 2001, the EU directive [[Units of Measure Directive|80/181/EEC]] stated that supplementary units (imperial units alongside metric including labelling on packages) would become illegal from the beginning of 2010.  In September 2007,<ref name="EUGivesUp"/> a consultation process was started which resulted in the directive being modified to permit supplementary units to be used indefinitely.

The third method is to redefine traditional units in terms of metric values.  These redefined "quasi-metric" units often stay in use long after metrication is said to have been completed.  Resistance to metrication in post-revolutionary France convinced Napoleon to revert to ''[[mesures usuelles]]'' (usual measures), and, to some extent, the names remain throughout Europe.  In 1814, Portugal adopted the metric system, but with the names of the units substituted by [[Portuguese customary units|Portuguese traditional ones]].  In this system, the basic units were the ''mão-travessa'' (hand) = 1&nbsp;[[decimetre]] (10&nbsp;''mão-travessas'' = 1&nbsp;''vara'' (yard) = 1&nbsp;metre), the ''[[canada (volume)|canada]]'' = 1&nbsp;litre and the ''libra'' (pound) = 1&nbsp;kilogram.<ref name=Fatima />  In the [[Netherlands]], 500&nbsp;g is informally referred to as a ''pond'' ([[Pound (mass)|pound]]) and 100&nbsp;g as an ''ons'' ([[ounce]]), and in Germany and France, 500&nbsp;g is informally referred to respectively as ''ein Pfund'' and ''une livre'' ("one pound").<ref>
{{cite web 
 |author=Hubert Fontaine 
 |title=Confiture de rhubarbe 
 |url=http://www.hubertlejardinier.com/confiture.htm 
 |access-date=5 November 2007 |archive-url=https://web.archive.org/web/20070928081538/http://www.hubertlejardinier.com/confiture.htm 
 |archive-date=28 September 2007 |language=fr 
 |url-status=dead 
}} "1 zeste de citron par livre (500g) de rhubarbe"</ref>

In Denmark, the re-defined ''pund'' (500&nbsp;g) is occasionally used, particularly among older people and (older) fruit growers, since these were originally paid according to the number of pounds of fruit produced.  In [[Sweden]] and [[Norway]], a ''mil'' ([[Scandinavian mile]]) is informally equal to 10&nbsp;km, and this has continued to be the predominantly used unit in conversation when referring to geographical distances.  In the 19th century, [[Switzerland]] had a non-metric system completely based on metric terms (e.g. 1&nbsp;''Fuss'' (foot) = 30&nbsp;cm, 1&nbsp;''Zoll'' (inch) = 3&nbsp;cm, 1&nbsp;''Linie'' (line) = 3&nbsp;mm).  In China, the ''[[catty|jin]]'' now has a value of 500&nbsp;g and the [[tael|liang]] is 50&nbsp;g.

Surveys are performed by various interest groups or the government to determine the degree to which ordinary people change to using metric in their daily lives. In countries that have recently changed, older segments of the population tend still to use the older units.<ref>{{Cite web |title=Metric or imperial: what measures do Britons use? {{!}} YouGov |url=https://yougov.co.uk/society/articles/41755-metric-or-imperial-what-measures-do-britons-use?redirect_from=%2Ftopics%2Fsociety%2Farticles-reports%2F2022%2F04%2F07%2Fmetric-or-imperial-what-measures-do-britons-use |access-date=2024-06-27 |website=yougov.co.uk |language=en-gb}}</ref>