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International Temperature Scale of 1990

October 15, 2023

The International Temperature Scale of 1990 (ITS-90) is an equipment calibration standard specified by the International Committee of Weights and Measures (CIPM) for making measurements on the Kelvin and Celsius temperature scales. It is an approximation of thermodynamic temperature that facilitates the comparability and compatibility of temperature measurements internationally. It defines fourteen calibration points ranging from 0.65 K to 1357.77 K (−272.50 °C to 1084.62 °C) and is subdivided into multiple temperature ranges which overlap in some instances. ITS-90 is the most recent of a series of International Temperature Scales adopted by the CIPM since 1927.[1] Adopted at the 1989 General Conference on Weights and Measures, it supersedes the International Practical Temperature Scale of 1968 (amended edition of 1975) and the 1976 "Provisional 0.5 K to 30 K Temperature Scale". The CCT has also published several online guidebooks to aid realisations of the ITS-90. The lowest temperature covered by the ITS-90 is 0.65 K. In 2000, the temperature scale was extended further, to 0.9 mK, by the adoption of a supplemental scale, known as the Provisional Low Temperature Scale of 2000 (PLTS-2000).[2]

Glass cell for Fixed point of water

In 2019, the kelvin was redefined. However, the alteration was very slight compared to the ITS-90 uncertainties, and so the ITS-90 remains the recommended practical temperature scale without any significant changes. It is anticipated that the redefinition, combined with improvements in primary thermometry methods, will phase out reliance on the ITS-90 and the PLTS-2000 in the future.[3]

Details Edit

The ITS-90 is designed to represent the thermodynamic (absolute) temperature scale (referencing absolute zero) as closely as possible throughout its range. Many different thermometer designs are required to cover the entire range. These include helium vapor pressure thermometers, helium gas thermometers, standard platinum resistance thermometers (known as SPRTs) and monochromatic radiation thermometers.

Although the Kelvin and Celsius temperature scales were (until 2019) defined using the triple point of water (273.16 K or 0.01 °C), it is impractical to use this definition at temperatures that are very different from the triple point of water. Accordingly, ITS-90 uses numerous defined points, all of which are based on various thermodynamic equilibrium states of fourteen pure chemical elements and one compound (water). Most of the defined points are based on a phase transition; specifically the melting/freezing point of a pure chemical element. However, the deepest cryogenic points are based exclusively on the vapor pressure/temperature relationship of helium and its isotopes whereas the remainder of its cold points (those less than room temperature) are based on triple points. Examples of other defining points are the triple point of equilibrium hydrogen (13.8033 K or −259.3467 °C) and the freezing point of aluminium (933.473 K or 660.323 °C).

The defining fixed points of the ITS-90 refer to pure chemical samples with specific isotopic compositions.[4] As a consequence of this, the ITS-90 contains several equations [5] [6][7] to correct for temperature variations due to impurities and isotopic composition.

Thermometers calibrated via the ITS-90 use complex mathematical formulas to interpolate between its defined points.[8] The ITS-90 specifies rigorous control over variables to ensure reproducibility from lab to lab. For instance, the small effect that atmospheric pressure has upon the various melting points is compensated for (an effect that typically amounts to no more than half a millikelvin across the different altitudes and barometric pressures likely to be encountered). The standard also compensates for the pressure effect due to how deeply the temperature probe is immersed into the sample. The ITS-90 also draws a distinction between “freezing” and “melting” points. The distinction depends on whether heat is going into (melting) or out of (freezing) the sample when the measurement is made. Only gallium is measured at its melting points; all other metals with defining fixed points on the ITS-90 are measured at their freezing points.

A practical effect of the ITS-90 is that the triple points and the freezing/melting points of its thirteen chemical elements are precisely known for all temperature measurements calibrated per the ITS-90 since these thirteen values are fixed by definition.

Limitations Edit

There are often small differences between measurements calibrated per ITS-90 and thermodynamic temperature. For instance, precise measurements show that the boiling point of VSMOW water under one standard atmosphere of pressure is actually 373.1339 K (99.9839 °C) when adhering strictly to the two-point definition of thermodynamic temperature. When calibrated to ITS-90, where one must interpolate between the defining points of gallium and indium, the boiling point of VSMOW water is about 10 mK less, about 99.974 °C. The virtue of ITS-90 is that another lab in another part of the world will measure the very same temperature with ease due to the advantages of a comprehensive international calibration standard featuring many conveniently spaced, reproducible, defining points spanning a wide range of temperatures.

Although “International Temperature Scale of 1990” has the word “scale” in its title, this is a misnomer that can be misleading. The ITS-90 is not a scale; it is an equipment calibration standard. Temperatures measured with equipment calibrated per ITS-90 may be expressed using any temperature scale such as Celsius, Kelvin, Fahrenheit, or Rankine. For example, a temperature can be measured using equipment calibrated to the kelvin-based ITS-90 standard, and that value may then be converted to, and expressed as, a value on the Fahrenheit scale (e.g. 211.953 °F).

ITS-90 does not address the highly specialized equipment and procedures used for measuring temperatures extremely close to absolute zero. For instance, to measure temperatures in the nanokelvin range (billionths of a kelvin), scientists using optical lattice laser equipment to adiabatically cool atoms, turn off the entrapment lasers and simply measure how far the atoms drift over time to measure their temperature. A cesium atom with a velocity of 7 mm/s is equivalent to a temperature of about 700 nK (which was a record cold temperature achieved by the NIST in 1994).

Estimates of the differences between thermodynamic temperature and the ITS-90 (T − T90) were published in 2010. It had become apparent that ITS-90 deviated considerably from PLTS-2000 in the overlapping range of 0.65 K to 2 K. To address this, a new 3He vapor pressure scale was adopted, known as PTB-2006. For higher temperatures, expected values for T − T90 are below 0.1 mK for temperatures 4.2 K – 8 K, up to 8 mK at temperatures close to 130 K, to 0.1 mK[3] at the triple point of water (273.1600 K), but rising again to 10 mK at temperatures close to 430 K, and reaching 46 mK at temperatures close to 1150 K.[9]

Standard interpolating thermometers and their ranges Edit

Lower (K) Upper (K) Variations Thermometer Calibration and interpolation strategy
0000.65 0003.2 01 Helium-3 vapor pressure thermometer Vapor pressure–temperature relationship fixed by a specified function.[10]
0001.25 0002.1768 01 Helium-4 vapor pressure thermometer Vapor pressure–temperature relationship fixed by a specified function.[11]
0002.1768 0005.0 01 Helium-4 vapor pressure thermometer Vapor pressure–temperature relationship fixed by a specified function.[12]
0003 0024.5561 01 Helium gas thermometer Calibrated at three fixed points in this range and interpolated in a specified way.[13]
0013.8033 1234.93 11 Platinum resistance thermometer Resistance calibrated at various fixed points and interpolated in a specified way.
Eleven distinct calibration procedures are specified.[14]
1234.93 03 Radiation thermometer Calibrated at one fixed point, and extrapolated according to Planck's law.
May be calibrated at Ag, Au, or Cu freezing point.[15]

Defining points Edit

The table below lists the defining fixed points of the ITS-90.

Substance and its state Temperature per ITS-90 Actual temperature
K °C °R °F K
Triple point of hydrogen 13.8033 −259.3467 24.8459 −434.8241
Triple point of neon 24.5561 −248.5939 44.2010 −415.4690
Triple point of oxygen 54.3584 −218.7916 97.8451 −361.8249
Triple point of argon 83.8058 −189.3442 150.8504 −308.8196
Triple point of mercury 234.3156 −38.8344 421.7681 −37.9019
Triple point of water[note 1] 273.16 0.01 491.69 32.02 273.1600(1) K
Melting point[note 2] of gallium 302.9146 29.7646 545.2463 85.5763
Freezing point[note 2] of indium 429.7485 156.5985 773.5473 313.8773
Freezing point[note 2] of tin 505.078 231.928 909.140 449.470
Freezing point[note 2] of zinc 692.677 419.527 1,246.819 787.149
Freezing point[note 2] of aluminium 933.473 660.323 1,680.251 1,220.581
Freezing point[note 2] of silver 1,234.93 961.78 2,222.87 1,763.20
Freezing point[note 2] of gold 1,337.33 1,064.18 2,407.19 1,947.52
Freezing point[note 2] of copper 1,357.77 1,084.62 2,443.99 1,984.32
  1. ^ The triple point of water is frequently approximated by using the melting point of water at standard conditions for temperature and pressure[citation needed].
  2. ^ a b c d e f g h Melting and freezing points are distinguished by whether heat is entering or leaving the sample when its temperature is measured. See melting point for more information.

See also Edit

References Edit

  1. ^ "Beginning in 1927, the CIPM, acting under the authority of the General Conference on Weights and Measures (CGPM) and, since 1937, on the advice of the Consultative Committee for Thermometry (CCT), has adopted a series of International Temperature Scales. Subsequent to the 1927 scale, new scales have been adopted in 1948, 1968, and 1990, with occasional minor revisions in intervening years."
  2. ^ "Considerable research has been conducted on establishing a temperature scale extending to temperatures lower than 0.65 K; the PLTS-2000 is the resulting outcome, defining temperature from 1 K down to 0.9 mK. The PLTS-2000 is explicitly a provisional scale, recognizing that the data sets comprising the basis of the scale were somewhat inconsistent below 10 mK. In the temperature range 0.65 K to 1 K, temperature may be defined on either the ITS-90 or the PLTS-2000. Either scale is acceptable; the choice of scale typically is dictated by convenience or the attainable uncertainty of realization. In rare cases where use of either scale is convenient, T2000 is a better approximation of thermodynamic temperature than T90 in the region of overlap." Consultative Committee for Thermometry, "Mise en pratique for the definition of the kelvin", 2011.
  3. ^ a b "Mise en pratique for the definition of the kelvin in the SI" BIPM, May 2019.
  4. ^ "Technical Annex for the International Temperature Scale of 1990 (ITS-90)". BIPM. 28 June 2017. Retrieved 24 June 2021.
  5. ^ "Technical Annex for the International Temperature Scale of 1990 (ITS-90)". BIPM. 28 June 2017. Retrieved 24 June 2021.
  6. ^ "Guide to the Realisation of the ITS-90 - Triple Point of Water". BIPM. 1 January 2018. Retrieved 24 June 2021.
  7. ^ "Guide to the Realisation of the ITS-90 - Fixed Points: Influence of Impurities". BIPM. 1 January 2018. Retrieved 24 June 2021.
  8. ^ "Guide to the Realisation of the ITS-90 - Platinum Resistance Thermometry". BIPM. 27 May 2021. Retrieved 24 June 2021.
  9. ^ Estimates of the Differences between Thermodynamic Temperature and the ITS-90 (2010)
  10. ^ "Guide to the Realisation of the ITS-90 - Vapour Pressure Scales and Pressure Measurements". BIPM. 1 January 2018. Retrieved 24 June 2021.
  11. ^ "Guide to the Realisation of the ITS-90 - Vapour Pressure Scales and Pressure Measurements". BIPM. 1 January 2018. Retrieved 24 June 2021.
  12. ^ "Guide to the Realisation of the ITS-90 - Vapour Pressure Scales and Pressure Measurements". BIPM. 1 January 2018. Retrieved 24 June 2021.
  13. ^ "Guide to the Realisation of the ITS-90 - Interpolating Constant-Volume Gas Thermometry". BIPM. 1 January 2018. Retrieved 24 June 2021.
  14. ^ "Guide to the Realisation of the ITS-90 - Platinum Resistance Thermometry". BIPM. 27 May 2021. Retrieved 24 June 2021.
  15. ^ "Guide to the Realisation of the ITS-90 - Radiation Thermometry". BIPM. 1 January 2018. Retrieved 24 June 2021.
  • Preston-Thomas H., Metrologia, 1990, 27(1), 3-10 (amended version).
  • "Mise en pratique for the definition of the kelvin" (PDF). Sèvres, France: Consultative Committee for Thermometry (CCT), International Committee for Weights and Measures (CIPM). 2011. Retrieved 25 June 2013.
  • Consultative Committee for Thermometry (CCT) (1989). "The International Temperature Scale of 1990 (ITS-90)" (PDF). Procès-verbaux du Comité International des Poids et Mesures, 78th meeting. Sèvres, France: International Committee for Weights and Measures (CIPM). Retrieved 25 June 2013.

External links Edit

  • ITS-90 (by Swedish National Testing and Research Institute)
  • About Temperature Sensors (information repository) 2018-12-16 at the Wayback Machine
  • NIST ITS-90 Thermocouple Database (by United States Department of Commerce, National Institute of Standards & Technology)
  • Conversion among different international temperature scales; equations and algorithms.
  • CIPM official publication of ITS-90 in 78th meeting in 1989
  • [1]

October 15, 2023
international, temperature, scale, 1990, equipment, calibration, standard, specified, international, committee, weights, measures, cipm, making, measurements, kelvin, celsius, temperature, scales, approximation, thermodynamic, temperature, that, facilitates, c. The International Temperature Scale of 1990 ITS 90 is an equipment calibration standard specified by the International Committee of Weights and Measures CIPM for making measurements on the Kelvin and Celsius temperature scales It is an approximation of thermodynamic temperature that facilitates the comparability and compatibility of temperature measurements internationally It defines fourteen calibration points ranging from 0 65 K to 1357 77 K 272 50 C to 1084 62 C and is subdivided into multiple temperature ranges which overlap in some instances ITS 90 is the most recent of a series of International Temperature Scales adopted by the CIPM since 1927 1 Adopted at the 1989 General Conference on Weights and Measures it supersedes the International Practical Temperature Scale of 1968 amended edition of 1975 and the 1976 Provisional 0 5 K to 30 K Temperature Scale The CCT has also published several online guidebooks to aid realisations of the ITS 90 The lowest temperature covered by the ITS 90 is 0 65 K In 2000 the temperature scale was extended further to 0 9 mK by the adoption of a supplemental scale known as the Provisional Low Temperature Scale of 2000 PLTS 2000 2 Glass cell for Fixed point of waterIn 2019 the kelvin was redefined However the alteration was very slight compared to the ITS 90 uncertainties and so the ITS 90 remains the recommended practical temperature scale without any significant changes It is anticipated that the redefinition combined with improvements in primary thermometry methods will phase out reliance on the ITS 90 and the PLTS 2000 in the future 3 Contents 1 Details 2 Limitations 3 Standard interpolating thermometers and their ranges 4 Defining points 5 See also 6 References 7 External linksDetails EditThe ITS 90 is designed to represent the thermodynamic absolute temperature scale referencing absolute zero as closely as possible throughout its range Many different thermometer designs are required to cover the entire range These include helium vapor pressure thermometers helium gas thermometers standard platinum resistance thermometers known as SPRTs and monochromatic radiation thermometers Although the Kelvin and Celsius temperature scales were until 2019 defined using the triple point of water 273 16 K or 0 01 C it is impractical to use this definition at temperatures that are very different from the triple point of water Accordingly ITS 90 uses numerous defined points all of which are based on various thermodynamic equilibrium states of fourteen pure chemical elements and one compound water Most of the defined points are based on a phase transition specifically the melting freezing point of a pure chemical element However the deepest cryogenic points are based exclusively on the vapor pressure temperature relationship of helium and its isotopes whereas the remainder of its cold points those less than room temperature are based on triple points Examples of other defining points are the triple point of equilibrium hydrogen 13 8033 K or 259 3467 C and the freezing point of aluminium 933 473 K or 660 323 C The defining fixed points of the ITS 90 refer to pure chemical samples with specific isotopic compositions 4 As a consequence of this the ITS 90 contains several equations 5 6 7 to correct for temperature variations due to impurities and isotopic composition Thermometers calibrated via the ITS 90 use complex mathematical formulas to interpolate between its defined points 8 The ITS 90 specifies rigorous control over variables to ensure reproducibility from lab to lab For instance the small effect that atmospheric pressure has upon the various melting points is compensated for an effect that typically amounts to no more than half a millikelvin across the different altitudes and barometric pressures likely to be encountered The standard also compensates for the pressure effect due to how deeply the temperature probe is immersed into the sample The ITS 90 also draws a distinction between freezing and melting points The distinction depends on whether heat is going into melting or out of freezing the sample when the measurement is made Only gallium is measured at its melting points all other metals with defining fixed points on the ITS 90 are measured at their freezing points A practical effect of the ITS 90 is that the triple points and the freezing melting points of its thirteen chemical elements are precisely known for all temperature measurements calibrated per the ITS 90 since these thirteen values are fixed by definition Limitations EditThere are often small differences between measurements calibrated per ITS 90 and thermodynamic temperature For instance precise measurements show that the boiling point of VSMOW water under one standard atmosphere of pressure is actually 373 1339 K 99 9839 C when adhering strictly to the two point definition of thermodynamic temperature When calibrated to ITS 90 where one must interpolate between the defining points of gallium and indium the boiling point of VSMOW water is about 10 mK less about 99 974 C The virtue of ITS 90 is that another lab in another part of the world will measure the very same temperature with ease due to the advantages of a comprehensive international calibration standard featuring many conveniently spaced reproducible defining points spanning a wide range of temperatures Although International Temperature Scale of 1990 has the word scale in its title this is a misnomer that can be misleading The ITS 90 is not a scale it is an equipment calibration standard Temperatures measured with equipment calibrated per ITS 90 may be expressed using any temperature scale such as Celsius Kelvin Fahrenheit or Rankine For example a temperature can be measured using equipment calibrated to the kelvin based ITS 90 standard and that value may then be converted to and expressed as a value on the Fahrenheit scale e g 211 953 F ITS 90 does not address the highly specialized equipment and procedures used for measuring temperatures extremely close to absolute zero For instance to measure temperatures in the nanokelvin range billionths of a kelvin scientists using optical lattice laser equipment to adiabatically cool atoms turn off the entrapment lasers and simply measure how far the atoms drift over time to measure their temperature A cesium atom with a velocity of 7 mm s is equivalent to a temperature of about 700 nK which was a record cold temperature achieved by the NIST in 1994 Estimates of the differences between thermodynamic temperature and the ITS 90 T T90 were published in 2010 It had become apparent that ITS 90 deviated considerably from PLTS 2000 in the overlapping range of 0 65 K to 2 K To address this a new 3He vapor pressure scale was adopted known as PTB 2006 For higher temperatures expected values for T T90 are below 0 1 mK for temperatures 4 2 K 8 K up to 8 mK at temperatures close to 130 K to 0 1 mK 3 at the triple point of water 273 1600 K but rising again to 10 mK at temperatures close to 430 K and reaching 46 mK at temperatures close to 1150 K 9 Standard interpolating thermometers and their ranges EditLower K Upper K Variations Thermometer Calibration and interpolation strategy000 0 65 000 3 2 0 1 Helium 3 vapor pressure thermometer Vapor pressure temperature relationship fixed by a specified function 10 000 1 25 000 2 1768 0 1 Helium 4 vapor pressure thermometer Vapor pressure temperature relationship fixed by a specified function 11 000 2 1768 000 5 0 0 1 Helium 4 vapor pressure thermometer Vapor pressure temperature relationship fixed by a specified function 12 000 3 00 24 5561 0 1 Helium gas thermometer Calibrated at three fixed points in this range and interpolated in a specified way 13 00 13 8033 1234 93 11 Platinum resistance thermometer Resistance calibrated at various fixed points and interpolated in a specified way Eleven distinct calibration procedures are specified 14 1234 93 0 3 Radiation thermometer Calibrated at one fixed point and extrapolated according to Planck s law May be calibrated at Ag Au or Cu freezing point 15 Defining points EditThe table below lists the defining fixed points of the ITS 90 Substance and its state Temperature per ITS 90 Actual temperatureK C R F KTriple point of hydrogen 13 8033 259 3467 24 8459 434 8241Triple point of neon 24 5561 248 5939 44 2010 415 4690Triple point of oxygen 54 3584 218 7916 97 8451 361 8249Triple point of argon 83 8058 189 3442 150 8504 308 8196Triple point of mercury 234 3156 38 8344 421 7681 37 9019Triple point of water note 1 273 16 0 01 491 69 32 02 273 1600 1 KMelting point note 2 of gallium 302 9146 29 7646 545 2463 85 5763Freezing point note 2 of indium 429 7485 156 5985 773 5473 313 8773Freezing point note 2 of tin 505 078 231 928 909 140 449 470Freezing point note 2 of zinc 692 677 419 527 1 246 819 787 149Freezing point note 2 of aluminium 933 473 660 323 1 680 251 1 220 581Freezing point note 2 of silver 1 234 93 961 78 2 222 87 1 763 20Freezing point note 2 of gold 1 337 33 1 064 18 2 407 19 1 947 52Freezing point note 2 of copper 1 357 77 1 084 62 2 443 99 1 984 32 The triple point of water is frequently approximated by using the melting point of water at standard conditions for temperature and pressure citation needed a b c d e f g h Melting and freezing points are distinguished by whether heat is entering or leaving the sample when its temperature is measured See melting point for more information See also EditThermodynamic absolute temperature the true temperature which ITS 90 is attempting to approximate Provisional Low Temperature Scale of 2000 PLTS 2000 A newer temperature scale for the range of 0 0009 K to 1 K based on the melting pressure of helium 3 Kelvin Triple point Vienna Standard Mean Ocean Water VSMOW Resistance thermometer Platinum resistance thermometer Planckian locus International Temperature Scale how successive revisions of the temperature scale have affected the relation between spectrum and temperature of a black bodyReferences Edit Beginning in 1927 the CIPM acting under the authority of the General Conference on Weights and Measures CGPM and since 1937 on the advice of the Consultative Committee for Thermometry CCT has adopted a series of International Temperature Scales Subsequent to the 1927 scale new scales have been adopted in 1948 1968 and 1990 with occasional minor revisions in intervening years Considerable research has been conducted on establishing a temperature scale extending to temperatures lower than 0 65 K the PLTS 2000 is the resulting outcome defining temperature from 1 K down to 0 9 mK The PLTS 2000 is explicitly a provisional scale recognizing that the data sets comprising the basis of the scale were somewhat inconsistent below 10 mK In the temperature range 0 65 K to 1 K temperature may be defined on either the ITS 90 or the PLTS 2000 Either scale is acceptable the choice of scale typically is dictated by convenience or the attainable uncertainty of realization In rare cases where use of either scale is convenient T2000 is a better approximation of thermodynamic temperature than T90 in the region of overlap Consultative Committee for Thermometry Mise en pratique for the definition of the kelvin 2011 a b Mise en pratique for the definition of the kelvin in the SI BIPM May 2019 Technical Annex for the International Temperature Scale of 1990 ITS 90 BIPM 28 June 2017 Retrieved 24 June 2021 Technical Annex for the International Temperature Scale of 1990 ITS 90 BIPM 28 June 2017 Retrieved 24 June 2021 Guide to the Realisation of the ITS 90 Triple Point of Water BIPM 1 January 2018 Retrieved 24 June 2021 Guide to the Realisation of the ITS 90 Fixed Points Influence of Impurities BIPM 1 January 2018 Retrieved 24 June 2021 Guide to the Realisation of the ITS 90 Platinum Resistance Thermometry BIPM 27 May 2021 Retrieved 24 June 2021 Estimates of the Differences between Thermodynamic Temperature and the ITS 90 2010 Guide to the Realisation of the ITS 90 Vapour Pressure Scales and Pressure Measurements BIPM 1 January 2018 Retrieved 24 June 2021 Guide to the Realisation of the ITS 90 Vapour Pressure Scales and Pressure Measurements BIPM 1 January 2018 Retrieved 24 June 2021 Guide to the Realisation of the ITS 90 Vapour Pressure Scales and Pressure Measurements BIPM 1 January 2018 Retrieved 24 June 2021 Guide to the Realisation of the ITS 90 Interpolating Constant Volume Gas Thermometry BIPM 1 January 2018 Retrieved 24 June 2021 Guide to the Realisation of the ITS 90 Platinum Resistance Thermometry BIPM 27 May 2021 Retrieved 24 June 2021 Guide to the Realisation of the ITS 90 Radiation Thermometry BIPM 1 January 2018 Retrieved 24 June 2021 Preston Thomas H Metrologia 1990 27 1 3 10 amended version Mise en pratique for the definition of the kelvin PDF Sevres France Consultative Committee for Thermometry CCT International Committee for Weights and Measures CIPM 2011 Retrieved 25 June 2013 Consultative Committee for Thermometry CCT 1989 The International Temperature Scale of 1990 ITS 90 PDF Proces verbaux du Comite International des Poids et Mesures 78th meeting Sevres France International Committee for Weights and Measures CIPM Retrieved 25 June 2013 External links EditThe Internet ITS 90 Resource by ISOTech Ltd ITS 90 by Swedish National Testing and Research Institute About Temperature Sensors information repository Archived 2018 12 16 at the Wayback Machine NIST ITS 90 Thermocouple Database by United States Department of Commerce National Institute of Standards amp Technology Conversion among different international temperature scales equations and algorithms CIPM official publication of ITS 90 in 78th meeting in 1989 1 Retrieved from https en wikipedia org w index php title International Temperature Scale of 1990 amp oldid 1177309670, wikipedia, wiki, book, books, library,

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