sentence: the ccu proposed to in addition to the speed of light , define four constants of nature -- planck 's constant , an elementary charge , boltzmann constant and avogadro constant -- to have exact values retire the international prototype kilogram revise the current definitions of the kilogram , ampere , kelvin and mole to make use of the above four constants of nature tighten the wording of the definitions of all the base units the cipm meeting of october 2010 found that '' the conditions set by the general conference at its 23rd meeting have not yet been fully met .