| 1st (1889) |
kilogram The kilogram is the base unit of mass in the International System of Units (SI, from the French Le Système International d’Unités),[Note 2] which is the modern standard governing the metric system. The kilogram is defined as being equal to the mass of the International Prototype Kilogram (IPK),[Note 3] which is almost exactly equal to the mass defined as mass of the international prototype kilogram (IPK) made of platinum Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements. A dense, malleable, ductile, precious, gray-white transition metal,-iridium Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second densest element (after osmium) and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts and and kept at the International Bureau of Weights and Measures The International Bureau of Weights and Measures , is an international standards organisation, one of three such organisations established to maintain the International System of Units (SI) under the terms of the Metre Convention (Convention du Mètre). The organisation is usually referred to by its French initialism, BIPM (Bureau international des poids et mesures), Sèvres Sèvres is a commune in the southwestern suburbs of Paris, France. It is located 9.9 km from the center of Paris, France. International prototype metre sanctioned. |
| 2nd (1897 1897 was a common year starting on Friday (link will display the full calendar) of the Gregorian Calendar (or a common year starting on Wednesday of the 12-day slower Julian calendar)) |
No resolutions were passed by the 2nd CGPM. |
| 3rd (1901 1901 was a common year starting on Tuesday (link will display calendar) of the Gregorian calendar (or a common year starting on Monday of the 13-day-slower Julian calendar). It was also the first year of the 20th century) |
litre The litre is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case (l and L). The lower case L is also often written as a cursive ℓ, though this symbol has no official approval by any international bureau. Although the litre is not an SI unit, it is accepted for use with the SI, and has appeared in several redefined as volume of 1 kg of water. Clarified that kilograms are units of mass, "standard weight" defined, standard acceleration of gravity Standard gravity, usually denoted by g0 or gn, is the nominal acceleration due to gravity at the Earth's surface at sea level, defined to be precisely 9.80665 m/s2 . This value was established by the 3rd CGPM (1901, CR 70) defined endorsing use of grams force and making them well-defined. |
| 4th (1907 1907 was a common year starting on Tuesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Monday of the 13-day-slower Julian calendar)) |
carat The carat is a unit of mass equal to 200 mg , and it is used for measuring gemstones and pearls = 200 mg adopted. |
| 5th (1913) |
International Temperature Scale proposed. |
| 6th (1921) |
Metre Convention revised. |
| 7th (1927) |
Consultative Committee for Electricity (CCE) created. |
| 8th (1933) |
Need for absolute electrical unit identified. |
| 9th (1948) |
ampere The ampere is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics. In practice, its name is often shortened to amp, bar Except for the power of ten, the definition of bar fits in the sequence of SI pressure units , namely, 1 bar ≡ 100,000 Pa = 100 kPa = 0.1 MPa. This is in contrast to the well-known unit of pressure, atmosphere, which now is defined to be 1.01325 bar exactly. As a rule of thumb, a bar is almost equal to an atmosphere, coulomb The coulomb is the SI derived unit of electric charge, and is approximately equal to the charge of 6.24151 × 1018 protons or −6.24151 × 1018 electrons. It is named after Charles-Augustin de Coulomb, farad The farad is the SI unit of capacitance. The term farad is named after the English physicist Michael Faraday, henry In physics, the henry is the SI unit of inductance. Originally the symbol was actually an upside down T but due to the fact no such symbol existed in standard typesets, the symbol was changed to a H. It is named after Joseph Henry (1797-1878), the American scientist who discovered electromagnetic induction independently of and at about the same, joule The joule , named after James Prescott Joule, is the derived unit of energy in the International System of Units. It is the energy expended in applying a force of one Newton through a distance of one metre (1 Newton·metre or N·m). In terms of dimensions:, newton The newton is the SI derived unit of force, named after Isaac Newton in recognition of his work on classical mechanics, ohm The ohm is the SI unit of electrical impedance or, in the direct current case, electrical resistance, named after Georg Simon Ohm, volt The volt is the SI derived unit of electromotive force, commonly called "voltage". It is also the unit for the related but slightly different quantity electric potential difference (also called "electrostatic potential difference"). It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the, watt The watt is a derived unit of power in the International System of Units (SI), named after the Scottish engineer James Watt (1736–1819). The unit measures the rate of energy conversion. It is defined as one joule per second, weber In physics, the weber is the SI unit of magnetic flux. A flux density of one Wb/m2 (one weber per square meter) is one tesla defined. Chose degree Celsius Celsius is a temperature scale that is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale two years before his death. The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval (a difference between two temperatures from among the three names then in use. l (lowercase L) adopted as symbol for litre. Both the comma and dot on a line are accepted as decimal marker symbols. Symbols for the stere The name originally comes from the Greek stereos, meaning solid. It was created in France in 1793 as a metric equivalent to the cord, for measuring large quantities of firewood and second The second , sometimes abbreviated sec., is the name of a unit of time, and is the International System of Units (SI) base unit of time. It may be measured using a clock changed [1]. The universal return to the Long Scale There are other numbering systems which are neither long nor short scale such as the Chinese numbering system, the Indian numbering system, the Japanese numbering system, and the Korean numbering system. Many countries, including most in continental Europe, use the long scale numbering system was proposed but not adopted. |
| 10th (1954) |
kelvin The kelvin is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale referenced to absolute zero, the absence of all thermal energy. So by definition, the temperature of a substance at absolute zero is zero kelvin (0 K). The secondary reference point on the Kelvin, standard atmosphere defined. International System of Units (metre The metre , symbol m, is the base unit of length in the International System of Units (SI). Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole, its definition has been periodically refined to reflect growing knowledge of metrology. Since 1983, it is defined as the distance travelled by light in, kilogram The kilogram is the base unit of mass in the International System of Units (SI, from the French Le Système International d’Unités),[Note 2] which is the modern standard governing the metric system. The kilogram is defined as being equal to the mass of the International Prototype Kilogram (IPK),[Note 3] which is almost exactly equal to the mass, second The second , sometimes abbreviated sec., is the name of a unit of time, and is the International System of Units (SI) base unit of time. It may be measured using a clock, ampere The ampere is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics. In practice, its name is often shortened to amp, kelvin The kelvin is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale referenced to absolute zero, the absence of all thermal energy. So by definition, the temperature of a substance at absolute zero is zero kelvin (0 K). The secondary reference point on the Kelvin, candela The candela is the SI base unit of luminous intensity; that is, power emitted by a light source in a particular direction, weighted by the luminosity function (a standardized model of the sensitivity of the human eye to different wavelengths, also known as the luminous efficiency function). A common candle emits light with a luminous intensity of) began. |
| 11th (1960) |
metre redefined in terms of wavelengths of light. Units: hertz The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of sine wave, particularly those used in radio and audio applications, lumen The lumen is the SI unit of luminous flux, a measure of the power of light perceived by the human eye. Luminous flux differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. The lumen is defined in relation to, lux The lux is the SI unit of illuminance and luminous emittance. It is used in photometry as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watts per square metre, but with the power at each wavelength weighted according to the luminosity function, a, tesla The tesla is the SI derived unit of magnetic field B (which is also known as "magnetic flux density" and "magnetic induction"). One tesla is equal to one weber per square meter, and it was defined in 1960 in honor of the Yugoslavian-American inventor, physicist, and electrical engineer Nikola Tesla. One billionth of a tesla is adopted. New metric system given the official symbol SI for Système International d'Unités, the "modernized metric system". Prefixes pico- Derived from the Italian piccolo, meaning small, this was one of the original 12 prefixes defined in 1960 when the International System of Units was established, nano- Nano- is a prefix in the metric system denoting a factor of 10−9 or 0.000000001. It is frequently encountered in science and electronics for prefixing units of time and length, such as 30 nanoseconds (symbol ns), 100 nanometres (nm) or in the case of electrical capacitance, 100 nanofarads (nF), micro- Micro is a prefix in the metric system denoting a factor of one millionth. Confirmed in 1960, the prefix comes from the Greek μικρός (mikrós), meaning "small", mega- Mega- is an prefix in the metric system denoting a factor of million. Confirmed in 1960, it comes from the Greek μέγας, meaning great, giga- The Oxford English Dictionary reports the earliest written use of giga in this sense to be in the Reports of the IUPAC 14th Conference in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga 109×" and tera- Confirmed in 1960, it comes from the Greek τέρας, meaning monster. It also bears a resemblance to the Greek prefix τετρα meaning four; the coincidence of it signifying the fourth power of 1000 served as a model for the higher-order prefixes peta, exa, zetta and yotta, all of which are deliberately distorted forms of the Latin or Greek confirmed. |
| 12th (1964) |
original definition of litre The litre is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case (l and L). The lower case L is also often written as a cursive ℓ, though this symbol has no official approval by any international bureau. Although the litre is not an SI unit, it is accepted for use with the SI, and has appeared in several = 1 dm³ restored. atto- Atto- is a prefix in the metric system denoting a factor of 10−18 or 0.000000000000000001 and femto- Femto- is a prefix in the metric system denoting a factor of 10−15 or 0.000000000000001. Adopted by the 11th Conférence Générale des Poids et Mesures, it was added in 1964 to the SI. It is derived from the Danish word femten, meaning "fifteen" prefixes. |
| 13th (1967) |
second redefined as duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C (83 °F), which makes it one of only five metals that are liquid at or near room temperature.[note 1] Caesium has physical and chemical properties similar to those of rubidium and potassium. The-133 atom at a temperature of 0 K. Degree Kelvin renamed kelvin. Candela redefined. |
| 14th (1971) |
new SI base unit mole defined. pascal, siemens approved. |
| 15th (1975) |
peta- and exa- prefixes. gray and becquerel radiological units. |
| 16th (1979) |
candela, sievert defined. Both l and L provisionally allowed as symbols for litre. |
| 17th (1983) |
metre redefined in terms of the speed of light, but keeps same length. |
| 18th (1987) |
conventional values adopted for Josephson constant, KJ, and von Klitzing constant, RK, preparing the way for alternative definitions of the ampere and kilogram. |
| 19th (1991) |
new prefixes yocto-, zepto-, zetta- and yotta-. |
| 20th (1995) |
SI supplementary units (radian and steradian) become derived units. |
| 21st (1999) |
new SI derived unit, the katal = mole per second, for the expression of catalytic activity. |
| 22nd (2003) |
a comma or a dot on a line are reaffirmed as decimal marker symbols, and not as grouping symbols in order to facilitate reading; "numbers may be divided in groups of three in order to facilitate reading; neither dots nor commas are ever inserted in the spaces between groups". [2]. |
| 23rd (2007) |
clarification about the kelvin and thoughts about possible revision of certain base units |
