On 16 November, scientists vote on whether to update the way we measure the kilogram. This week, Ian Sample investigates the history of the metric system, and finds out how universal constants might now make it more robust

On 16 November, scientists will vote on whether or not to update the way we measure the kilogram and three other base units. Currently the kilogram is defined by a cylinder of platinum-iridium, locked in a vault in a suburb of Paris. But few have access to it, and the international copies are ever so slightly shifting their weight relative to it.

The hope now is to move away from this unstable, physical artefact and instead base our definition of mass on a fundamental constant of nature – Planck’s constant. If this goes through, the whole metric system will for the first time be derivable from natural phenomena.

This week, Ian Sample speaks to metrologist Prof Stephan Schlamminger, a physicist at the National Institute of Standards and Technology who has spent the last seven years getting ever more precise measurements for Planck’s constant. We also hear from two members of the National Physical Laboratory: Stuart Davidson, who shows our producer the British national standard kilogram, and Fiona Auty, who gives us some of the history of the metric system.