SafekipediaMetrology
Adapted from Wikipedia · Adventurer experience
Metrology is the scientific study of measurement. It helps us understand and use units, like meters and kilograms, so everyone agrees. This is important because it connects many human activities, from building houses to making medicine.
The idea of modern metrology began during the French Revolution. Leaders wanted everyone to use the same units, so they created the metric system in 1795. This system uses decimals, which makes calculations easier. Over time, many countries started using it too. To make sure everyone’s measurements matched, the Bureau International des Poids et Mesures (BIPM) was created through the Metre Convention. This led to the International System of Units (SI) in 1960.
Metrology has three main jobs: defining units, creating real-world examples of those units, and making sure all measurements can be traced back to standard references. It helps in science, industry, and even laws about how measurements are used. Each country has its own network of labs and facilities to support these efforts, which helps with fair trade and many parts of daily life.
History
See also: History of measurement
Having a way to measure things is important, and everyone needs to agree on what measurements mean. One of the oldest records of a standard measurement comes from around 2900 BC in Egypt. The measurement, called the royal Egyptian cubit, was based on the length of a pharaoh's forearm plus the width of his hand. Copies of this standard were given to builders, which helped make structures like the pyramids very evenly sized.
Other places, like China, also had important ways to measure things. Even after big empires like Rome and Greece fell, people still needed ways to measure, but it was hard because different places used different systems. In 1196, England created rules for measuring lengths, and later, in 1215, the Magna Carta included rules for measuring drinks like wine and beer.
Modern ways of measuring began during the French Revolution. Leaders wanted everyone in France to use the same measurements, so they created a new standard based on nature. In 1791, they defined the metre, which led to the metric system in 1795. This system was later adopted by many countries. To help all countries use the same standards, the International Bureau of Weights and Measures was created. Over time, this system was updated and is now known as the International System of Units (SI).
Subfields
Metrology is the science of measurement. It helps us understand and use units correctly, which is important for many activities. It includes defining units, creating ways to measure them, and making sure measurements can be traced back to standard references.
There are three main areas of metrology. Scientific metrology focuses on creating accurate measurement standards and methods. Applied metrology uses measurements in industries to make sure products are good quality. Legal metrology deals with rules about measurements to keep people safe and ensure fair trade.
Concepts
The International System of Units (SI) has seven basic units for measuring things like length, mass, and time. All other units come from these basic ones. Now, scientists use natural constants, like the speed of light, to define these units. This makes sure measurements stay the same everywhere and always.
When we measure something, we need to know how sure we are about that measurement. This is called measurement uncertainty. It tells us a range where the true value likely is. For example, if we say a pencil is 15.0 ± 0.1 cm long, we are pretty sure the real length is between 14.9 cm and 15.1 cm. This helps scientists and engineers know how much they can trust their measurements.
A standard is a special object or tool that helps us compare measurements. There are different levels of standards, from the very best ones kept in labs to the ones we use every day. This way, everyone can be sure their measurements match up, no matter where they are in the world.
Measurement uncertainty tells us how much a measurement might differ from the true value. It has two parts: the range of possible values and how confident we are that the true value lies within that range. Usually, scientists use a confidence level of 95%, meaning there is a high chance the true value is within the range they give. This helps make sure measurements are accurate and reliable.
| Base quantity | Name | Symbol | Definition |
|---|---|---|---|
| Time | second | s | The duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom: 130 |
| Length | metre | m | The length of the path travelled by light in a vacuum during a time interval of 1/299792458 of a second: 131 |
| Mass | kilogram | kg | Defined (as of 2019) by "... taking the fixed numerical value of the Planck constant, h, to be 6.62607015×10−34 when expressed in the unit J s, which is equal to kg m2 s−1 ...": 131 |
| Electric current | ampere | A | Defined (as of 2019) by "... taking the fixed numerical value of the elementary charge, e, to be 1.602176634×10−19 when expressed in the unit C, which is equal to A s ...": 132 |
| Thermodynamic temperature | kelvin | K | Defined (as of 2019) by "... taking the fixed numerical value of the Boltzmann constant, k, to be 1.380649×10−23 when expressed in the unit J K−1, which is equal to kg m2 s−2 K−1 ...": 133 |
| Amount of substance | mole | mol | Contains (as of 2019) "... exactly 6.02214076×1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol−1 ...": 134 |
| Luminous intensity | candela | cd | The luminous intensity, in a given direction, of a source emitting monochromatic radiation of a frequency of 540×1012 Hz with a radiant intensity in that direction of 1/683 watt per steradian: 135 |
International infrastructure
Several international groups help make sure measurements all around the world are the same and fair.
Metre Convention
The Metre Convention started three important groups to help with measurements. The first is the General Conference on Weights and Measures (CGPM). It brings together leaders from many countries to talk about new ideas for measurements. The second is the International Committee for Weights and Measures (CIPM). It gives advice about measurements to the CGPM. The third is the International Bureau of Weights and Measures (BIPM). It helps the other two groups and keeps special tools for measuring.
General Conference on Weights and Measures
The General Conference on Weights and Measures is the main group that makes big decisions. Leaders from many countries meet every few years to talk about new ways to make measurements better. The last meeting was in November 2018. They talked about changing some important measurements, and the new ways started on May 20, 2019.
International Committee for Weights and Measures
The International Committee for Weights and Measures has eighteen smart scientists from different countries. They help the CGPM with important questions about measurements. They meet once a year in Sèvres, France, to talk about what other groups are doing and to give advice.
International Bureau of Weights and Measures
The International Bureau of Weights and Measures is in Sèvres, France. It keeps very special tools used for measuring and helps the other groups. It also keeps records of important measurements.
International Organization of Legal Metrology
The International Organization of Legal Metrology started in 1955 to help countries make sure their measurement rules are the same. This helps when countries trade with each other. The group makes suggestions and guidelines to help countries create good rules for measurements.
International Laboratory Accreditation Cooperation
The International Laboratory Accreditation Cooperation (ILAC) helps make sure that groups that check measurements work the same way all over the world. It started in 1977 and in 2000, 36 members agreed to accept each other's work. This means that if a lab in one country checks a measurement, other countries will trust that check too.
Joint Committee for Guides in Metrology
The Joint Committee for Guides in Metrology (JCGM) makes guides to help people understand measurements better. It works with eight other groups, including the International Electrotechnical Commission, the International Organization for Standardization, and the International Union of Pure and Applied Chemistry. The JCGM has two groups that work on different guides.
National infrastructure
A national measurement system is a network of labs and groups that help a country keep its measurements accurate and consistent. This system makes sure that measurements in one country match up with those in other countries. Many countries are part of an agreement called the CIPM Mutual Recognition Arrangement.
Metrology institutes
A national metrology institute helps a country keep its measurements accurate by setting standards and comparing measurements with other countries. Examples include the National Institute of Standards and Technology in the United States and the National Physical Laboratory (United Kingdom).
Calibration laboratories
Calibration labs check and adjust tools used in factories and offices to make sure they give correct measurements. They are approved by authorities and connect companies back to national standards.
Accreditation bodies
An organization is approved, or accredited, when a special group checks that it can do its job well. For this to be accepted worldwide, the group must follow international rules. Examples include the National Association of Testing Authorities in Australia.
Impacts
Metrology helps us in many parts of life, like with money, energy, the environment, health, making things, and keeping products safe to buy. It is very important for countries to trade fairly with each other. When everyone uses the same measurements for things like water, fuel, food, and electricity, it makes buying and selling easier and keeps people safe.
Accurate measurements can save lives. Tools like radar guns and breathalyzers work better because of metrology. It also helps doctors measure the human body more accurately, which makes healthcare better and saves money. Good measurements are important for understanding things like climate change and for making rules to protect the environment. Metrology gives strong support for new ideas to grow.
Related articles
This article is a child-friendly adaptation of the Wikipedia article on Metrology, available under CC BY-SA 4.0.
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