The kilogram is no longer dead weight

The kilogram has been around since the beginning of the 18th Century; and despite the 200 plus years of its existence, there has been no significant change to it. At least, that was the case prior to May 20th, 2019, when the kilogram was officially redefined using an unchanging, fundamental constant called the Planck constant. This made the kilogram the last in a long series of SI units that have made this historic transition. Matthew Hall spoke with Richard  Brown, the head of metrology at the National Physical Laboratory (NPL) here in the UK, who shed some light on the significance of World Metrology day...