The International system of scientific units is having a shake-up; with four of the basic measurement units (the ampere, kilogram, kelvin and mole), all set for redefinition. If the General Conference of Weights and Measures agrees with the recommendations brought to them by the International Bureau of Weights and Measures, then any changes would take place in May of that year.
The changes will allow every unit to be defined against a constant, with a fixed value. This will resolve issues such as the Kilogram’s relationship to a piece of Platinum-irridium which is kept in Paris. Over the century during which this has been used as a standard for a kilogram, it has been exposed to air and can lose or gain atoms, thereby creating discrepancies. Using constants instead will resolve uncertainties in defining units and therefore enable scientists working to high levels of precision to do so in multiple ways, at any place or time and on any scale, without losing accuracy.
For further information on this proposed change, and some diagrams that explain the changes in detail, please visit:
https://www.nature.com/news/new-definitions-of-scientific-units-are-on-the-horizon-1.22837
A recent review article;
Quantum-based vacuum metrology at the National Institute of Standards and Technology has recently been published, please visit:
https://doi.org/10.1116/1.5033568
