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International Temperature Scale of 1990

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.

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2019 redefinition of the SI base units

In 2019, four of the seven SI base units specified in the International System of Quantities were redefined in terms of natural physical constants, rather than human artifacts such as the standard kilogram.

Aluminium

Aluminium is a chemical element with the symbol Al and atomic number 13.

Helium-3

Helium-3 is a light, non-radioactive isotope of helium, consisting of two protons and one neutron.

Helium-4

Helium-4 is a stable isotope of the element helium.

Hydrogen

Hydrogen is a chemical element with the symbol H and atomic number 1.

Kelvin

Kelvin is a unit of temperature widely used in the scientific field.

National Institute of Standards and Technology

The National Institute of Standards and Technology (NIST) is a federal agency in the United States that develops and promotes measurement standards, guidelines, and technology to enhance productivity, support innovation, and improve the competitiveness of businesses.

Oxygen

Oxygen is a chemical element with the symbol O and atomic number 8.