By the Numbers



Adam Bender

Extremely accurate measurements and the standards they inform are the foundations of trade, commerce and the technology we take for granted in our everyday lives.

In a sense, metrology makes the world go around.

It can quantify how long it takes the Earth to rotate, and the science of weights and measurements underpins everything from telling time to ensuring the fairness of international trade agreements.

Metrologists must be extremely precise in their measurements, according to Alan Steele, Canada's chief metrologist and the general manager of Measurement Science and Standards at the National Research Council of Canada.

The best clocks can now tell time with an error that would be equivalent to less than one second over the lifetime of the universe. Meanwhile, temperature and force are measured on a parts-per-million basis, and length and electricity are measured at a parts-per-billion level.

As Canada's official metrology institute, the NRC covers "everything to do with the metric system at the highest level of realization of the basic units of the measurement system," says Steele.

The NRC is responsible for Canada's official time and keeps the country's prototype for the kilogram, a small cylinder of platinum iridium metal. The agency's metrology portfolio also includes electrical power measurements for utilities, technologies used for calibrations in cancer treatment, and chemical measurements used for testing organic substances and the environment.

Metrology is inextricably tied to the standards work of organizations like ASTM International, supporting key efforts such as building quality infrastructure, says Steele. "There's a natural linkage between developing standards in a process-based organization like ASTM with the measurements for making sure everything turns out right."

International Trade

Having common, agreed on measurement standards eases international trade and reduces cost between parties.

"The harmonization of measurement becomes a part of the fabric of an international trading framework," says Steele. Metrology is integral to trade because "almost always, you're buying an amount of something."

Standard and accurate measurements provide an "evidence basis to fairness," he says. "You want to know that you're getting what you pay for."

Standards grounded in sound metrology also enable the interoperability of parts, which allows products like the Airbus A380 jet to be assembled from components built in many different countries.

"That simply wouldn't work if the measurement system didn't agree in all of those countries," Steele says.

Everyday Life

Metrology also underpins everyday actions in people's lives, says Steele. For example, consistent weight measurements ensure that supermarket shoppers pay the right price for meat and vegetables. And measurements are important to quality of life, with metrologic-based environmental testing that ensures water is clean to drink.

In healthcare, improvements in measurement and calibration of linear accelerators used in clinical therapies have increased cancer survival rates.

"When you know a more accurate dose to use when irradiating a patient, the survivability rate goes up very, very sharply," says Steele. "That's because if you were giving too much dose compared to what you thought, you would be killing healthy cells which could kill the patient with radiation poisoning. But if you were giving too little dose, you wouldn't be giving enough energy to kill the cancer cells, and then the cancer would win."

Another everyday example is accurate measurement of time. Not only does accurate time help people get to work on a standardized schedule, but it also enables valuable technologies like the Global Positioning System, which powers location tracking in smartphones.

GPS relies on a constellation of satellites that carry atomic clocks synchronized to each other and to atomic clocks on the ground. A GPS-enabled device receives the time signals from several satellites at different known locations in orbit and uses the small differences in time caused by the differences in the distance to each satellite to triangulate its current location on earth.

"That wouldn't work at all if the time signal was no good," says Steele.

International Cooperation

As neighbors and trading partners, Canada and the United States have forged strong collaboration on metrology issues. The NRC works closely with the U.S. National Institute of Standards and Technology, and experts from both countries are involved in ASTM International.

"NIST and NRC have cooperated extensively and productively in the field of international metrology for many years," says James Olthoff, Ph.D., director of the NIST Physical Measurement Laboratory.

"We have had a number of exchange visits of scientific staff over the years to share knowledge of physical measurement techniques. Recently, the two laboratories have worked closely to raise the profile and quality of metrology in chemistry."

Steele says, "We often share the same view."

Already, experts from both countries are leading the way on watt-balance measurements to determine what is called "Planck's constant," which will be used to redefine the kilogram in 2018.

Currently, the SI unit of mass is defined by a small cylinder of platinum iridium metal. "We'll be getting rid of the last material man-made artifact as a defining quantity for the international system of units," says Steele.

The new, physics-based definition will rely on Planck's constant (from quantum mechanics) that links the energy and oscillation frequency of photons. NIST and NRC are working together on watt balance experiments, as well as several educational events, to prepare the world for the redefinition, says Olthoff.

Also in 2018, the ampere (electricity), kelvin (temperature) and mole (quantity of matter) are due to be updated at the General Conference on Weights and Measures, the international meeting of the Convention of the Meter.

Preparing for this change has been a major focus for the NRC, which participates in many scientific and technical committees organized by the International Bureau of Weights and Measures, the treaty organization created in 1875 to provide the structure for member governments to act together on matters related to units of measurement.

Steele says, "There's a lot of activity going on in the background to do our very best work on - quite frankly – the most difficult measurement problems in the world. We must make sure that we know the value of these constants in such a way so that when we make the transition in 2018, no one will really notice. Commerce and trade will continue without disruption, but scientists will be able to continue their quest to improve measurement techniques and, in turn, our understanding of the world around us."

Adam Bender is a freelance writer based in Philadelphia, Pennsylvania.

January/February
2016
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