At each conference, members take decisions, generally based on reports from the International Committee for Weights and Measures, which proposes improvements to the International System of Units (SI). The fundamental change to the SI came in 2018, when four of the seven base units were redefined and the other definitions reformulated (see the article *A new definition of the international system of units, in Tangente* special issue 69). These major changes took 20th-century theories into account—particularly relativity and quantum physics: the quantum kilogram is now defined in terms of the Planck constant.
This year, although no fundamental changes were made, the conference emphasized the importance of adapting the SI to the digital age, adopting new prefixes to meet the need to express quantities of digital information larger than 10 24. Four prefixes were therefore added to the SI: ronna for 10 27, ronto for 10 -27, quetta for 10 30, and quecto for 10 -30.
Ronnagrams and quettametres will make it possible to express quantities on scales ranging from microscopic to enormous, with up to thirty zeros before or after the decimal point. This is the first time the SI, established in 1960, has adopted new prefixes! Thus, the Earth weighs about six ronnagrams. By convention, prefixes for large multiples end in "a", while those for very small fractions end in "o".
