International Temperature Scale of 1990

The International Temperature Scale of 1990 (ITS-90) is a way of measuring temperatures. It is based on a set of specific temperatures, like the freezing point of water (0 °C) and the boiling point of water (100 °C). By measuring the temperature of things using these fixed points as a reference, it's easier to compare temperatures from place to place. For example, if two people use the same thermometer in two different places, they'll get the same reading.