Changes

As the metric system has changed over time, some units have been abandoned and replaced with others. Examples of obsolete metric units, which should not be used.

As the metric system has changed over time, some units have been abandoned and replaced with others. Examples of obsolete metric units, which should not be used.

* The '''calorie''' was originally defined as the amount of [[energy]] required to raise 1 g of water through 1 °C. It later was clarified to raising the temperature from 15 °C to 16 °C, since the energy required varies slightly with temperature. Confusingly, a second calorie, the Calorie (spelt with an upper case C) was introduced that was defined as the amount of energy required to raise 1 kg of water through 1 °C. Thus , 1 Calorie = 1000 calories. The Calorie (big C) became widely used as a measure of food energy. To avoid the confusion the Calorie was renamed the kilocalorie and the term Calorie was deprecated. The kilocalorie has now been replaced by the joule as the unit of energy, though energy values in kilocalories are still widely seen.

* The '''calorie''' was originally defined as the amount of [[energy]] required to raise 1g of water through 1°C. It later was clarified to raising the temperature from 15°C to 16°C, since the energy required varies slightly with temperature. Confusingly, a second calorie, the Calorie (spelt with an upper case C) was introduced that was defined as the amount of energy required to raise 1 kg of water through 1 °C. Thus , 1 Calorie = 1000 calories. The Calorie (big C) became widely used as a measure of food energy. To avoid the confusion the Calorie was renamed the kilocalorie and the term Calorie was deprecated. The kilocalorie has now been replaced by the joule as the unit of energy, though energy values in kilocalories are still widely seen.

* The '''Ångstrom''' was a very small unit of length equal to 10^-10 m. It was used for describing the wavelength of light, for example. The ångstrom was replaced by the nanometer. 1 nm = 10 Å.

* The '''Ångstrom''' was a very small unit of length equal to 10^-10 m. It was used for describing the wavelength of light, for example. The ångstrom was replaced by the nanometer. 1 nm = 10 Å.

* The '''curie''' (symbol Ci, for [[Marie Curie]]) is an obsolete unit of radioactivity. Its original definition was "the amount of radioactivity in one gram of [[radium]]-226." Madame Curie, of course, is most famous as the discoverer of radium. It was replaced by the becquerel, though it is still widely used in the US nuclear power industry. One curie is equal to 3.7 * 10¹⁰ becquerel.

* The '''curie''' (symbol Ci, for [[Marie Curie]]) is an obsolete unit of radioactivity. Its original definition was "the amount of radioactivity in one gram of [[radium]]-226." Madame Curie, of course, is most famous as the discoverer of radium. It was replaced by the Becquerel, though it is still widely used in the US nuclear power industry. One curie is equal to 3.7 * 10¹⁰ Becquerel.

* The '''micron''' (symbol µ) was a unit of length equal to one thousandth of a millimeter. It was replaced by the micrometer (symbol µm) in 1960.

* The '''micron''' (symbol µ) was a unit of length equal to one thousandth of a millimeter. It was replaced by the micrometer (symbol µm) in 1960.

[http://www.bipm.org/en/si/si_brochure/ The official, definitive definition of the SI system, from the Bureau Internationale des Poids et Mesures]

[http://www.bipm.org/en/si/si_brochure/ The official, definitive definition of the SI system, from the Bureau Internationale des Poids et Mesures]

[http://physics.nist.gov/Pubs/SP811/contents.full.html Guide to the SI System from NIST, the lead federal agency on all metrology issues for the US]

[http://physics.nist.gov/Pubs/SP811/contents.full.html Guide to the SI System from NIST, the lead federal agency on all meteorology issues for the US]