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Game over for the kilo

open this image in new window: Metal weights

This article was published on 11 May 2018

As the world prepares for the historic redefining of the kilogram, Callaghan Innovation scientists have come up with a uniquely Kiwi solution.

At a glance

  • This year’s World Metrology Day will be the last for ‘the big K’, a lump of metal kept under glass in Paris that has defined the kilogram for 129 years.

  • Instead scientists will use quantum physics to define a standard kilo.

  • New Zealand’s Measurement Standards Laboratory (MSL) has developed an unprecedented ‘desktop’ version of the instrument required to do the measuring.

  • MSL is holding a special World Metrology Day event on May 22 to herald the changes to the kilogram and other units of measurement.

The kilogram has developed a weight problem.

Affectionately known as ‘the big K’ or ‘le grand K’, the kilogram is literally a little cylinder of metal kept in a vault in Paris. Whenever you go to the supermarket and buy a kilo of cheese, your purchase is based on this one 129-year-old artefact half a world away.

But the big K is showing its age. Its weight has shifted over time, and the world scientific community has decided that quantum physics must come to the rescue and redefine the kilo.

“It’s crazy to have a system of measurement based on something that’s not stable, so every time it changes the definition of mass in the universe changes,” says Fleur Francois, director at New Zealand’s national metrology institute, Measurement Standards Laboratory (MSL).

This year’s international World Metrology Day on May 20 will be the big K’s last. In November, the General Conference on Weights and Measures at Versailles is expected to ratify a new definition for the kilogram based on measuring a constant of nature (the Planck constant).  At the same time, similar new definitions will be agreed for the ampere (electric current), the kelvin (temperature) and the mole (amount of substance).  The changes are due to come into effect on World Metrology Day 2019.

If metrologists (measurement scientists) do their job properly, the average person won’t notice a thing.  In true Kiwi style the MSL team has come up with a unique solution to meet New Zealand’s needs.

MSL scientist Dr Chris Sutton and his colleagues have created a desktop version of a super-precise instrument called a Kibble Balance for producing the New Zealand primary kilogram. 

Assembling New Zealand's Kibble Balance
Assembling New Zealand's Kibble Balance

In the Northern Hemisphere they have the gold-plated version, Fleur says. “They’ve got this thing that cost millions and takes up two storeys of a building.

“Here all we need is a device that allows us to plug in a natural constant of nature along with other variables, and from this calculate a kilogram to a high enough accuracy for our needs.”

The Kiwi Kibble Balance will be the only one in this part of the world, with some other Southern Hemisphere countries likely to rely on it for their measurements. The invention contributed to Chris Sutton winning one of metrology’s top international awards last year.

To mark this year’s historic World Metrology Day, MSL is holding a programme of events on Tuesday May 22nd at Callaghan Innovation’s Gracefield innovation quarter, the home of the MSL Kibble Balance.

“We’re keen to get people along so they can hear what’s happening in the measurement world and the opportunities these changes will provide for advancement,” Fleur says.

The changes to the kilo and other measurement units are important because they impact practically every industry, from aviation and beverages to natural gas and pharmaceuticals, and in the long term may enable new technologies, Fleur says.

“For me, when I think about space exploration – and who knows, we might colonise Mars one day – we’re going to need to be able to measure mass to great accuracy.”

For more information visit the MSL website or contact MSL on

About MSL

The Measurement Standards Laboratory of New Zealand (MSL) is the country’s national metrology institute and a business unit of Callaghan Innovation. It ensures that New Zealand’s units of measurement are consistent with the International System of Units, the SI. It employs around 35 scientists, technicians and engineers based at Gracefield, Lower Hutt. It provides its clients with the most accurate calibration service in the country for a wide range of instruments and artefacts and provides advice and training to ensure the equipment is used effectively.