I addition to use of calories (in Concepts of Science) I also define one
meter in the way it used to be. Why should the speed of light be part of
my vocabolary at this stage? And one second is defined in terms of this
big celestial clock of Copernicu and Newton. Why should I be distracted
by molecular oscillations? And my kilogram is ...., as you may guess.
I see no harm in using old units. I will discredit caloric substance in
the same lecture in which the unit is defined. And I would emphasize that
"we can define a unit, and start using it in predictions, without knowing
that what used to be called heat is now viewed as a form of energy".