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International Practical Temperature Scale

British  

noun

  1. a temperature scale adopted by international agreement in 1968, and revised in 1990, based on thermodynamic temperature and using experimental values to define 16 fixed points. The lowest is the triple point of an equilibrium mixture of orthohydrogen and parahydrogen (–259.34°C) and the highest the freezing point of copper (1084.62°C)

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