20/05/2019 - Today, May 20, 2019, we inaugurate the new definition of the kilogram (kg) of the International System of Units (SI). From now on the kilogram is no longer defined by the mass of the International Kilogram Prototype (IPK), a cylinder made of platinum-iridium alloy stored in the International Bureau of Weights and Measures in Saint-Cloud, France, to be defined by a relation based on the Planck constant. This change solves the problem that had arisen because the standard kilogram was an unstable unit, since it was detected that it was varying in magnitude, losing mass over time.

Now it defined by an universal quantum constant, with which the value of the kg is fixed and unalterable. The calculation of the value of the kg is based on the Planck constant and thus resolves the uncertainty posed on this unit of mass, fundamental both in the scientific and economic areas.

We are witnessing a historic event and we say goodbye to the International Kilogram Prototype (IPK), which has been the pattern for 130 years, defined at the General Conference on Weights and Measures of 1889, and we welcome the new definition of the remaining kg linked to Planck's constant!