Future developments Metric system

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relations between proposed si units definitions (in colour) , 7 fundamental constants of nature (in grey) fixed numerical values in proposed system.


after metre redefined in 1960, kilogram si base unit relied on specific artefact. after 1996–1998 recalibrations clear divergence between international , various national prototype kilograms observed.


at 23rd cgpm (2007), cipm mandated investigate use of natural constants basis units of measure rather artefacts in use. @ meeting of ccu held in reading, united kingdom in september 2010, resolution , draft changes si brochure presented next meeting of cipm in october 2010 agreed in principle. ccu proposed to



in addition speed of light, define 4 constants of nature—planck s constant, elementary charge, boltzmann constant , avogadro constant – have exact values
retire international prototype kilogram
revise current definitions of kilogram, ampere, kelvin , mole make use of above 4 constants of nature
tighten wording of definitions of base units

the cipm meeting of october 2010 found conditions set general conference @ 23rd meeting have not yet been met. reason cipm not propose revision of si @ present time . cipm did sponsor resolution @ 24th cgpm in changes agreed in principle , expected finalised @ 25th cgpm in 2014.








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