Revising the SI - news, updates and events
On World Metrology Day we celebrated the launch of the redefined SI. Thanks to everyone who attended our Roadshow events to learn more about this significant change to the way the global measurement standards are realised.
Throwing the Kilogram Competition
Throughout the SI Roadshow events we ran a Competition to see who could guess how far our 1 kilogram reference standard could be thrown. This has now closed and results have been published on our Competition page.
International System of Units Redefinition, 2019
The International System of Units, known as the SI, is the globally-agreed basis for expressing measurements at all levels of precision, and in all areas of science, technology, and human endeavour.
The SI is presently made up of seven base quantities that each correspond to a universally-recognised unit.
The SI will undergo a major revision in May 2019 that will be implemented by the international measurement community. This global change involves moving away from material artefacts (e.g. the kilogram prototype in Paris), and instead employing a set of seven defining constants, from which all units can be derived.
The Measurement Standards Laboratory is the primary agency responsible for implementing the new SI definitions into New Zealand. Adopting the definitions will allow NZ to remain consistent with international best practice and allow precision measurement to be available to everyone.
Four of the base units – the kilogram, ampere, kelvin, and mole – will be redefined based on fixed numerical values of the Planck constant (h), the elementary charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively. The three remaining base units – the second, metre and candela – are already defined by physical constants, so it will only be necessary to edit their present definitions.
The SI has been revised several times since its formal adoption by the CGPM in 1960. However, redefining four base units at one time is unprecedented, requiring simultaneous world-wide collaborations in diverse fields of metrology. As in the past, care has been taken to ensure that there will be no perceptible impact on daily life and that measurements made with previous definitions of the units remain valid within their measurement uncertainties. Few users outside national metrology laboratories will notice the changes.
Why do we need the SI?
- For fair domestic and international trade, so when you buy or sell a quantity of something you and your customers know what you are getting without being cheated or surprised.
- So that things made in different places, countries, or even factories across the street will fit and work together.
- To provide a common basis to communicate measurements in science, engineering, health, safety and the public good.
Want to know more?
You can download a handy factsheet on the changes here [PDF, 373 KB].
Read our Press Release here.
Read more about each of the measurement units here.
Read our case study 'Quantum Balancing Act for the SI'
Read 'Information for users about the revision of the SI' (external link)from the BIPM website.