World Metrology Day

May 17, 2017 — Ottawa, Ontario

Celebrating the science of measurement

Suppose you build lawnmowers. The blades are held in place by 10 millimetre bolts. You get a good price on them from a company in another country. When they arrive, you find that none of them fits the 10 millimetre holes you've drilled in your lawnmowers.

Actually, that's very unlikely to happen, and that's just one reason World Metrology Day is worth celebrating.

The making of the metre (and the kilogram, and the second, etc.)

Metrology is the science of measurement, and World Metrology Day marks the signing of the Metre Convention, also known as the Treaty of the Metre, on May 20, 1875. The treaty established the International Committee for Weights and Measures (CIPM) to work on ensuring global uniformity in units of measurement.

Importantly, the treaty also proposed the first international standards for the metre and the kilogram. Until then, there was no widespread agreement on either—and agreement in measurement has an importance that goes well beyond making sure nuts and bolts fit together. Everything from the safety of the medications we take to the regulations that protect us from over-exposure to potentially dangerous chemicals relies on accurate, standard measurement. Metrology is behind the standards that ensure you get what you pay for when you fill your car with gas or pick up a couple steaks for the barbecue.

The science of measurement?

Yes, metrology is very scientific; it has to be to keep up with and enable advances in science and technology. The metre, for example, was once defined by a metal bar in Paris. Today, a metre is defined by how far light travels through a vacuum in 1/299,792,458 of a second. This is, unsurprisingly, directly related to the speed of light, being 299,792,458 meters/second—nearly 300,000 km/s.

In fact, the kilogram is the only standard measure still defined by an artefact—the so-called "Golden K"—a lump of platinum-iridium alloy locked away in a vault in Paris. Like all physical things, its mass is not perfectly stable, and will change over time. Other units of measurement are now based on fundamental constants—things that are defined by nature that don't vary—the way the speed of light is used to define the metre.

Canada helping to redefine the kilogram

The global community is expected to settle on a new definition for the kilogram by the end of 2018, and National Research Council Canada (NRC) is making an important contribution to this effort.

At NRC, researchers in Metrology have used a highly sensitive scale called a Watt, or Kibble balance named after its inventor Dr. Bryan Kibble, to measure the electrical force needed to counterbalance a weight, linking it to the Planck constant. This is a unit so small that exact measurement is extremely difficult to achieve, but NRC has it down to an uncertainty of fewer than 10 parts per billion. To put it in context, the Kibble balance was able to “see” an earthquake in Virginia from its underground bunker in Ottawa. This sensitivity, as well as all the related measurements and calibrations, are what make this experiment so difficult and why it is widely considered one of the five hardest known to science. Defining the Planck constant paves the way for the kilogram's redefinition in exceedingly precise terms.

When the NRC says "exact time", it's not kidding

NRC Metrologists work with the Standards Council of Canada to ensure all of Canada's measurements are consistent with international standards. From mass to length, NRC can measure it with mind-boggling precision, including time.

Since designing one of the world's first atomic clocks in 1958, NRC scientists have been refining their work to the point where they are accurate to within three seconds of error over a million years. In other words, your watch would have to be adjusted by about 12 minutes if you set it when dinosaurs first walked the earth. They are currently working on installing a new type of clock that will be up to 100 times more accurate than that.

Close enough doesn't count

Such precise time-keeping is more than scientific curiosity—it underpins everything from the elaborate network switching protocols that enable the Internet to the GPS so many of us now take for granted. GPS calculates your position using the times it takes for electromagnetic signals to reach several GPS satellites. Since those signals are travelling at the speed of light, the clocks in those satellites must be exceptionally accurate and precisely coordinated—for the navigation of ships and planes especially, as even a miniscule variation could lead to significant and potentially dangerous errors in positioning.

It's all about structure

Metrology provides the structure that allows modern life to go on in a safe and orderly fashion. Without standard, accurate measurement, modern life could get pretty chaotic. As we rely more and more on technology working accurately and reliably on our behalf, the work Metrologists do, even if it’s in the background, can be seen everywhere. Taken to the extreme, recipes wouldn’t come out reliably, and neither would diets that rely on correct portion sizing. Pilots would never be sure if their planes were overloaded or, well, going in the right direction. We'd never know if we were breaking the speed limit or the sound barrier. We'd think we were on time for lunch, but our date might accuse us of being late.

And parts for our lawnmowers might fit—or they might not. In the world of metrology, size matters.

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