this invention relates to a method for determining the absolute temperature of a substance , comprising the steps of : sensing the absolute temperature of the substance and generating an absolute value associated therewith ; sensing a temperature difference between the temperature of a reference body and the temperature of the substance and generating a difference value associated therewith ; determining an optimised value of the absolute temperature of the substance by means of said absolute value and said difference value . the invention also relates to an apparatus for performing the method ; a temperature control system for controlling the temperature of a substance ; and an instrument comprising a substance , and such a temperature control system .