Soon every scientific text and curriculum worldwide will have to be rewritten, as the basic language of science - the SI system of units - is fundamentally reformed. The Quantum-SI will finally remove the last 'fetish object' (the International Prototype Kilogramme, a 19th Century cylinder of Platinum-Iridium alloy, kept in a vault in Paris) from the interlinked definition of SIs 7 base units - metre, kg, second, mole, kelvin, ampere, and candela (or maybe 6, if they abandon the candela). All will then rely upon universal physical constants, and the conception of the 18th Century savants who conceived the whole grand idea (evolved through the Metre Convention into the present SI system) will finally be fully realised. Snag is, the definition of those units will then be nigh-on incomprehensible to anyone except a physicist. And there will be no appeal. Jeffrey Williams, former Editor of the journal Metrologia and head of publications at the Bureau Internationale des poids et mesures, which administers the SI System for the world, explains it brilliantly (and not without a certain mordant humour) in his comprehensive and clearly, for him, cathartic historical treatment.