is: a temperature scale based on heat flow under carefully controlled conditions.
is also: perhaps the most fundamental of all temperature scales. [P7.2]
rarely is used: in practice, since it is essentially identical to the far more practical ideal gas absolute temperature scale over a very wide range of temperatures. [P7.2]
is defined: by the thermometric relation
where 
is the quantity of heat that flows in or out of a system at temperature 
in a reversible isothermal process that links one adiabat to another, and 
is the quantity of heat that flows in or out if the system in a reversible isothermal process at the triple-point temperature (defined to be 
) that returns the system from the second adiabat to the first. [P7.2]
Copyright 1997, The Open University