Abstract :
In 2005, the CIPM, in accepting CCT Recommendation T3, made a substantial
change in the definition of the quantity ‘temperature’ by transforming the
written standards for temperature (the “temperature scales”) into implementations of
the mise en pratique of the kelvin. Having considered “that the creation of a formal
mise en pratique of the definition of the kelvin would considerably simplify and clarify
statements and recommendations of the CCT concerning the realization of the
definition of the kelvin and the implementation of practical temperature scales,” the
CIPM decision transformed the present ITS-90 and PLTS-2000 into two ways to implement
the mise en pratique, with the possibility to further define “in due course” in
the mise en pratique “recommendations concerning the direct determination of thermodynamic
temperature.” The paper presents the author’s views regarding possible
implications for the concept of a mise en pratique when applied to the kelvin beyond
the present implementation. One possibility is to promote the formal use and status
of realizations of the thermodynamic scale that, in practice, today only represents the
physical basis of an empirical scale like the ITS-90. Another path arises from assuming
that the only technical limit placed on the addition of further methods to the mise
en pratique is that they be compatible with one another, to avoid ambiguities in the
definition of the temperature values, though without the constraint of having the same,
or comparable, accuracy. As a consequence, other scales that are currently considered
‘approximations’ to the ITS-90, with no formal status other than possibly being ‘recommended’
by some official body, such as the CCT WG2, could be upgraded to im-
