Some reflections on the proposed redefinition of the unit for the amount of substance and of other SI units.

Proposals on the floor at CIPM are aiming at defining basic units by stipulating a consensus value for a number of fundamental constants. The paper indicates the author's viewpoint about a number of issues that, in his view, should be better understood before such a choice becomes indisputable. They include the count nature of the Avogadro number; the correct expression of its stipulated numerical value; the check for the consistency of the SI system; the shift to the unit of the experimental uncertainty; the loss of the concept of base unit; the possibility of checking the correctness of the future standards; implications for the future reductions in uncertainty; the meaning of 'fundamental' related to the constants; and some lexical problems. [ABSTRACT FROM AUTHOR]