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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 that derived from the United Kingdom), to the metric or SI (Système International) system.1 Introduction
1.1 Situation
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.
SI is based on the MKS (Metre-Kilogram-Second) division of metric measurements. For a while there was heated contention with the CGS (Centimeter-Gram-Second) and some areas of science still use this form of the system, even though it is not the international standard any more. Either way, one wonders why there was no meter-gram-second configuration that 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.
1.2 Time
The metric system has the second as its base unit of time. The minute, hour and day are officially "non-SI units accepted for use with the International System", even though for strict scientific use the SI recommends only the second and decimal multiples of the second. So for example, kilometres per hour is an accepted unit of speed in the metric system, but metres per second would be preferred in a scientific setting.
The metric or decimal hour is one tenth of a day/night cycle, and is thus equivalent to 2 hours, 24 minutes in common units. It is divided into 100 metric minutes, each one equivalent to 1 minute, 26.4 seconds in common units. The metric hour was originally a part of the plan of metrication first introduced in France during the French Revolution. However, unlike the other metric units (such as the metre and the kilogram), it failed to gain popular acceptance. It was never widely used, and the plan was dropped during the rule of Napoléon Bonaparte. A similar fate befell the metric unit for practical angular measurement, the grade, later renamed the gon, which divides the full angle into 400 units (instead of 360, 2π or 1).
1.3 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. Therefore the knot, which is nautical miles per hour, remains the prime unit of velocity for maritime and air navigation.
For aircraft flying, altitudes are almost universally calculated from air pressure to feet (in steps of 100) rather than metres. Since aircraft pilots and air traffic controllerAir traffic controllers are persons who operate the air traffic control system to expedite and maintain a safe and orderly flow of air traffic and help prevent mid-air collisions. They apply separation rules to keep each aircraft apart in their area of res 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 airforces (mainly, but not only former Warsaw PactHeinz Hoffmann, Polish Premier Wojciech Jaruzelski, Warsaw Pact Commander in Chief Viktor Kulikov, and Czechoslovakian Defence Minister Martin Dzur discussing Warsaw Pact manoeuvres in Poland, March 1981. The Warsaw Pact or Warsaw Treaty was a military al) are using metres, however.
