This day coincides with the celebration of the World Metrology Day, a milestone for scientific progress, as important changes come into force in the definition of the units of measurement of the International System following the relevant vote for its revision, which took place on 16/11/2018.
None of the units of measurement refers to physical objects anymore and the currently established definitions of the units of measurement of mass (kg), current (ampere, A), temperature (kelvin, K) and quantity of the substance (mol) are redefined on the basis of global physical constants.

For more information on the changes please refer to the BIPM website

The ninth version fully describing the International System of Units is also available: The International System of Units (SI)

As far as the chemical measurement community is concerned, the molar is redefined based on Avogadro number, while the kilo is redefined based on the Plank constant. Especially for the new definition of mole, you can refer to the following link: The Mole (presented by Martin Milton)

According to the head of the International Bureau of Weights and Measures, Dr Martin Milton, "the changes aim at a more stable background, which will be a springboard for the promotion of scientific knowledge, the development of new technologies and the response of the scientific community to the great societal challenges of our time."