Development of SI Proposed redefinition of SI base units

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mass drift on time of national prototypes k21–k40, plus 2 of international prototype kilogram s (ipk s) sister copies: k32 , k8(41). mass changes relative ipk.


the 9th cgpm (1948) instructed cipm make recommendations single practical system of units of measurement, suitable adoption countries adhering metre convention .


the recommendations based on mandate presented 11th cgpm (1960) formally accepted , given name système international d unités , abbreviation si .





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