Metric system
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).
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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; 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.
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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. [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. [8]
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Notes and references
- ^ Metric system 'was British' - from the BBC video news
- ^ Metrication timeline, by Pat Naughtin, PDF referenced on 18 May 2008
- ^ 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.. Retrieved on 2007-04-12.
- ^ 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. Retrieved on 2007-04-12.
- ^ "Jet's Fuel Ran Out After Metric Conversion Errors", New York Times, July 30, 1983. Retrieved on 2007-08-21. "Air Canada said yesterday that its Boeing 767 jet ran out of fuel in midflight 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. Retrieved on 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."
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See also
- Binary prefix
- SI prefix
- Conversion of units
- Metric yardsticks—easy-to-remember rules of thumb
- Metrication
- ISO 31—metric writing style
- Metric time
- History of measurement
- Units of measurement
- Metrology
- Orders of magnitude
- UTC—Coordinated Universal Time
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