  The cosmological constant, usually named Lambda, was introduced by Einstein
in 1917 and abandoned by him as his biggest "blunder". It currently seems to
make a spectacular comeback in the framework of the new cosmological standard
model. One will explain why, together with the Planck's constant, the
Boltzmann's constant, the celerity of light and the Newton's constant, also
considered by Einstein, the cosmological constant may play a foundational role
in the conceptual framework, an in the metrological framework a role comparable
with the one attributed to Avogadro constant
