Short answers, pulled from the story.
The first coherent metric system was devised by chemists Antoine and Anne-Marie Lavoisier during the French Revolution (1789-1799), initially for the Ferme generale. Their work built on ideas proposed by Gabriel Mouton, a priest of the Collegiate Church of St Paul in Lyon, who outlined a decimal measurement system anchored to the Earth's dimensions in the 1660s-1670s.
The General Conference on Weights and Measures proclaimed the International System of Units in 1960. At that time the metre was redefined using the wavelength of a spectral line of the krypton-86 atom, and the standard metre artefact from 1889 was retired.
The SI defines seven base units: the metre (length), kilogram (mass), second (time), ampere (electric current), kelvin (thermodynamic temperature), mole (amount of substance), and candela (luminous intensity). All other physical quantities are expressed as combinations of these seven.
The old kilogram standard, a platinum-iridium cylinder held in France, had diverged from its replicas by 50 micrograms since fabrication, making the unit accurate to no better than 5 parts in a hundred million. In May 2019, the kilogram was redefined in terms of the Planck constant, anchoring it to a fundamental physical quantity rather than a physical object.
The United States is the most prominent country that has not fully adopted the metric system. Although the US uses SI in scientific and many industrial contexts, everyday commerce continues to rely on different units for distance, weight, and volume.
The katal is a derived SI unit for catalytic activity, equivalent to one mole per second (1 mol/s). It was added to the International System of Units in 1999 and is the most recently introduced named derived unit in the SI.