Future developments Metric system
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 unit...