Why has the kilogram been redefined after nearly 130 years?
Since 1889, a kilogram was defined by a platinum-iridium cylinder prototype housed near Paris. The prototype's weight was found to fluctuate as it picks up microparticles of dirt and was thus deemed unreliable. Hence, scientists on Friday, chose the Planck constant, a fundamental constant of nature, to end dependence on a physical object for the SI unit of mass.