Thermodynamic temperature the properties of a particular material; two that it refers to an absolute zero according to the properties of the ideal gas. The International System of Units specifies a particular scale for thermodynamic temperature. It uses the kelvin scale for measurement and selects the triple point of water at 273.16 K as the fundamental fixing point. Other scales have been in use historically. The Rankine scale, using the degree Fahrenheit as its unit interval, is still in use as part of the English Engineering Units in the United States in some engineering fields. ITS-90 gives a practical means of estimating
Absolute zero where "S" is the entropy. In such a circumstance, pure substances can (ideally) form perfect crystals as "T" → 0. Max Planck's strong form of the third law of thermodynamics states the entropy of a perfect crystal vanishes at absolute zero. The original Nernst "heat theorem" makes the weaker and less controversial claim that the entropy change for any isothermal process approaches zero as "T" → 0: The implication is that the entropy of a perfect crystal simply approaches a constant value. The Nernst postulate identifies the isotherm T = 0 as coincident with the adiabat S = 0, although