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The measure of all things

Hands-on at the exhibit

  • Get involved in seven interactives representing each of the SI base units, including:
  • Use a laser interferometer to measure length (SI unit: metre)
  • Try a Kibble balance to weigh samples (SI unit: kilogram)

Find out more

The shifting foundation stones of SI measurements are about to be anchored for good.

The International System of Units (SI) is humanity’s chosen method to measure the physical world, and it’s about to go through the most profound change in its 200-year history. At this exhibit you’ll get hands-on with all seven SI measures and consider the impact of such a revolutionary change. 

Measurement is at the heart of all science and engineering, but accuracy is limited by uncertainty in the definitions of SI units. For instance, the UK standard for all mass measurements is a metal cylinder stored at the National Physical Laboratory. Over time, atoms may be accumulating on it, or being sloughed off, to subtly change its mass. So, from May 2019, all the SI units – the kilogram, second, metre, kelvin, ampere, candela and mole – will be redefined in terms of natural constants (Planck’s constant, in the case of the kilogram).  This change will ensure the SI unit definitions remain stable indefinitely, underpinning accurate science, trade and industry.

Presented by the National Physical Laboratory.