Published by Australian Academy of Science
A fair cop! Accurate breath analysis and speed detection Box 1 | Measurement standards

We have an extraordinary capacity to measure things precisely. We can measure the speed at which stars are moving, we can measure the mass of atoms, and timing a race to the nearest one-hundredth of a second is no problem at all.

But are these measurements accurate? Ultimately, accuracy depends on the reliability of the measuring device (and the competence of the operator). To make sure the measuring device is reliable, it needs to be calibrated periodically by other measuring devices, which in turn must also be calibrated. Sound complicated? It is, but there is a system in place to make it work.

The national measurement system

In Australia, the national measurement system ensures that measurements are made on a consistent basis throughout the country – not just those made by the police but also in commerce, industry, science, engineering, international trade, health and safety. It guarantees ‘traceability’ – which means that the steps taken to calibrate an instrument through a hierarchy of calibrations of increasingly higher accuracy can be traced back to the appropriate Australian primary standard, which in turn is linked to an international standard agreed to by most nations of the world.

The national measurement system comprises six national organisations along with state and territory measurement authorities and is coordinated by the National Standards Commission, a Commonwealth Statutory Authority established in 1950. The basic objective is to ensure that measurements are based on good science and the instruments that make them are reliable. And if the court asks for proof of this, the measurements are traceable to a reliable source.

Related site

• Australia's measurement system (National Measurement Institute)

Other boxes

Box 2. Drager Alcotest 7110