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news3The kilogram is now defined in terms of the Planck constant, guaranteeing long-term stability of the SI mass scale. The kilogram can be realized by any suitable method, (for example the Kibble (watt) balance or the Avogadro (X-ray crystal density) method). Users are able to obtain traceability to the SI from the same sources used as before (the BIPM, national metrology institutes and accredited laboratories). International comparisons will ensure their consistency. The value of the Planck constant was chosen to ensure that there was no change in the SI kilogram at the time of redefinition. The uncertainties offered by NMIs to their calibration customers will also be broadly unaffected.