Short answers, pulled from the story.
The International System of Units, known as SI, is the fundamental language of science, technology, industry, and global commerce. This system is coordinated by the International Bureau of Weights and Measures, an organization established under the Metre Convention of 1875.
The International System of Units includes seven base units: the second for time, the metre for length, the kilogram for mass, the ampere for electric current, the kelvin for thermodynamic temperature, the mole for the amount of substance, and the candela for luminous intensity. These units are defined by fundamental constants of nature such as the hyperfine transition frequency of caesium-133 and the Planck constant.
The redefinition of the kilogram was adopted at the 26th General Conference on Weights and Measures on the 16th of November 2018 and came into effect on the 20th of May 2019. This change shifted the definition from the physical International Prototype of the Kilogram to the Planck constant.
The International System of Units provides twenty-four metric prefixes ranging from yotta, which represents 10^24, to yocto, which represents 10^-24. These prefixes allow scientists to express quantities of any magnitude as multiples or sub-multiples of base units by powers of ten.
The International System of Units evolved from the centimetre-gram-second system of units developed in the 1860s and the MKSA system approved in 1946. The SI system was officially adopted in 1960 by the 11th General Conference on Weights and Measures to replace incompatible regional units.