Experts meet in London to redefine the kilogram

The Independent : On Monday scientists gathered in London at the Royal Society, the UK’s national academy of science, to present their progress on redefining the kilogram. It has been based since 1889 on the mass of a solid cylinder of platinumiridium alloy locked in a vault in Sèvres, France. The kilogram is the only international standard unit of measurement that is based on a physical object rather than a fundamental physical constant. Scientists now believe, however, that it is time to redefine the kilogram because there is evidence that the precise mass of the international prototype in Sèvres is not as constant as it should be.