The importance of measuring
How big, how heavy, how long, how small, how...? Measuring is deeply rooted in us humans. We want to know which car is the fastest, who is the longest and who is the strongest. The importance of measuring correctly and equally cannot be underestimated.
We have always measured. In the past, measurements were often based on the human body, such as the width of a thumb or the length of an arm. But since the width of a thumb differs from person to person, this was not a sustainable solution. When many countries signed Meter Convention in 1875, important steps were taken towards a common international system of measurement units, what we today call the SI.
“Basically, the SI is a prerequisite for trading. As the geographical area of trade expanded, from the immediate area to trade between countries and continents, common units for measurement became increasingly important. It is not possible to trade if you do not agree on the units of measurement. Today, the SI and metrology are a foundation of all parts of society and in all areas”, says Jan Johansson who is responsible for the National Laboratories for the different physical quantities at RISE.
You cannot know the true value
What is a good measurement? How do we ensure that we measure correctly and that we measure in the same way? A basic premise is this: You can never know that the value you measured is the true value.
"There are many factors that affect measurements. How hard you pull the tape measure, temperature and humidity, the properties of the object we are measuring and so on. The only thing we can be sure of when we measure is that we can never know that we have measured the true value", says Jan Johansson.
We can never know for certain that the measured value is the true value.
In metrology this is called measurement uncertainty. Sometimes the measurement uncertainty does not matter that much. It doesn't really matter if you are 187 or 189 cm tall. But when it comes to trade and manufacturing, it is more important. The component for the car must fit and you want the gas pump to show the correct value when you fill up.
"And sometimes it can even be a matter of life and death, such as when it comes to dosing medicine. Measurements are the basis for making decisions in different ways, and to make good decisions we need to have a good grasp of our measurement methods and the quality of the measurement", says Jan Johansson.
RISE is responsible for traceability
Another fundamental concept in metrology is traceability. It is the traceability that makes a meter a meter or a kilogram a kilogram all over the world. As the National Metrology Institute of Sweden, RISE is responsible for maintaining the traceability of most physical quantities through several National Laboratories.
"Traceability means that there must be a chain of comparisons all the way from the vegetable scale in the store up to a national standard, with specified measurement uncertainties. You can picture it as a pyramid where measuring devices all over the world are calibrated and can be traced to a single reference or standard", says Jan Johansson.
Calibration is the act of comparing a measuring device against a reference or a standard that is calibrated against another standard all the way up to a national standard. For each calibration step down the pyramid, the measurement uncertainty increases. The National Laboratories are responsible for maintaining national standards and a big part of the research at the National Laboratories concerns developing standards with even lower measurement uncertainty than today.
"We do this to meet the increased demands from industry and business. The demands on accuracy are increasing all the time. An example of this is that recently new prefixes within the SI system was added for 1027 and 1030, i.e. 27 and 30 zeros, to meet the future needs for accuracy", says Jan Johansson.
Is there a limit on how accurately can we measure?
"I don't know how many times I've said that we've reached the limit and been wrong, so now my answer is that I don't see a definite limit. But it is important to remember that a good measurement does not mean that it has as small measurement uncertainty as possible, but that the measurement uncertainty is known and that it is adapted to the needs of the measurement. If the production process requires a measurement uncertainty of a tenth of a second, it makes no sense to deliver a measurement uncertainty of a billionth of a second."
National Metrology Institute and National Laboratories
As the National Metrology Institute of Sweden RISE maintains metrological traceability through the National Laboratories for different physical quantities. Chains of calibrations, national standards and international comparisons makes certain that a kilogram is a kilogram and a meter a meter everywhere.