| Abstract | Since its inception in 1927, the International Temperature Scale has changed to meet the needs of the time in a predictable, evolutionary fashion. Occasionally, the changes to its basis formulation could be considered revolutionary. The ITS protocol specifies phase transitions with assigned temperatures (the defining fixed points), defining instruments (thermometers), and interpolating (or extrapolating) equations. Over time, the selection of fixed points and their assigned temperatures have changed, defining instruments have been added and deleted, and the equations have undergone change, particularly for the temperature range defined by the platinum resistance thermometer. |
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