A list of fixed temperatures is given. This list has been produced by national laboratories from all over the world. It has been approved by the B.I.P.M. (Bureau Internationale des Poids et Mesure) in Paris. Temperatures between the fixed points can be measured, using a platinum resistance thermometer (up to 660 °C). This thermometer, however, has to be calibrated first. This is being done at a number of fixed temperatures, covering the desired range. Procedures and formulae for defining an interpolating thermometer are given as well.