Hi! I ran across an odd item on a review exam of some sort - a multiple choice item that asked for a label that applied to boiling point (BP) and melting point (MP) for any or all substances. The best answer seems to be “fixed points” but I have been unable to locate a term that applies as generally as used for this item. Specifically, with respect to water at one atmosphere, BP and MP have been used as fixed points to establish Fahrenheit and Celsius systems for measuring temperature. Have BP and MP for other substances also been referred to as “fixed points”? I can’t find a citation or reference. Any input? Thanks!!