Since 1889, kilogram is defined by a platinum-iridium alloy cylinder that we know as Le Grand K. This international determiner of kilogram is kept in a vault with three layers of lock underneath Pavillon the Breteuil which was unveiled by King Louis XIV in 1672.
Barry Inglis, President of the International Committee for Weights and Measures, however, has changed the definition of Kilogram to something more fundamental, defined by atomic-detail numbers instead of an inconsistent tangible human object. SI-based units have been officially changed on May 20, 2019, on the 144th anniversary of Metre Convention.
We now use Planck constant to define kilogram and here’s the new definition: 6.626 x 10-34 joule seconds. It is also equal to the weight of 1.4755214 x 1040 photons.
The reason for the change is scientifically logical; Le Grand K does not have a constant weight due to atomic particles that are constantly moving and changing. You don’t touch it with bare hands, hands in gloves, or anything but a special tool. Nevertheless, the 130-year model cannot be eternal.
In fact, the original Le Grand K is lighter than its copies. Yet, the speed of the light traveling through space does not change.
Ampere is now defined by the elementary charge of a proton, Kelvin by Boltzmann constant, Meter by Avogradro constant and Candela by photometric spectral luminous efficacy concept.
Does this mean weighing the right amount of salt to put for seasonings is going to change? Not really. This subtly more precise measurement is meant for scientists who are always dreading the constantly changing weight of the cylinder. They need something precise and eternal; a coefficient that will never change forever.