The International Temperature Scale (known as ITS-90) was agreed in 1990 and fixed the triple point of water (where water, ice and water vapour coexist in equilibrium) as 273.16 K by definition. Many other fixed points are used to define the scale over a wide temperature rangesuch as the freezing point of gold at 1337.33 K and the triple point of hydrogen at 13.8033 K. At lower temperatures the vapour pressure of liquid helium is used.
Some of the temperatures in this article are shown on the logarithmic temperature scale below.
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