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Simply put, metrology is the of measure- International System of Units—SI ment and its application. It includes all theoretical In the United States of America, there are two and practical aspects of , at any measurement systems in use: the U. S. Custom- level of in any field of application. We ary System and the International System of Units, all use metrology dozens of a week. If you known as the SI. The U.S. Customary System is have measured cream in your coffee or used an used in mainly commercial and personal activities alarm or pumped into your car, you ap- (, , cup, etc.), while the SI is used in sci- plied metrology principles. Metrology deals with ence, medicine, industry sectors and some making accurate, repeatable with of government. The SI is used by most countries a known level of uncertainty. exclusively; indeed it is the foundation of our History worldwide measurement system. The SI has seven base units as defined in the chart below. The measurements we take for granted today started as far back as 3000 BC in ancient Egypt with the use of the Royal Cubit which was the Base quantity SI SI symbol Meter m length of the pharaoh’s arm from bent elbow to kg the tip of his middle finger. A master cubit was s crafted in granite and subsequent tools cre- A ated from the master cubit. As you can imagine, Thermodynamic K this wasn’t a sustainable measurement system. mol Which pharaoh created the tool? Did succeeding Luminous cd pharaoh’s change the measurement unit to match their forearms? Did measurement confusion reign As an evolving system, the SI is updated and with each new pharaoh? improved as technology permits. For example, up until 1960, the base unit meter was based on a Fast forward a couple of thousand when - rod cast in 1889. Now, seventeen nations met in Paris in 1875 for the it is defined as a constant of nature—the distance Convention (Convention du Mètre), to travels in a during one period of establish a permanent organizational structure , corresponding to the transition be- to act in common accord on all matters relat- tween two hyperfine levels of the of ing to units of measurement. The Treaty of 1875 the cesium-133 . This defines the meter as has some 58 government signatories today. The the distance light travels in 1/299 792 458th of a treaty established three essential organizations: second. CGPM—General Conference on and Effective , 2019, the CGPM passed a Measures: The main decision-making body com- resolution redefining the kilogram based on a posed of member states constant of nature, the , which would remove the risk of referencing a single, CIPM—International Committee for Weights and delicate artifact. Measures: Advises the CGPM on technical mat- ters of metrology

BIPM—International Bureau of Weights and Measures: Operates under the CGPM and CIPM and maintains the SI—International System of Units Redefining the kilogram will have repercussions- measurement instruments. especially for derived units. Derived units are Applied, Technical or, Industrial metrology quantities we are all familiar with, use daily and, includes traceability to the SI to ensure confi- are made up of products and powers of SI units. dence in measurement. Measurement can be de- Looking at the last column in the chart below, one fined as the process of experimentally obtaining can appreciate how redefining the kilogram, or one or more quantity values that can reasonably any base unit for that matter, can have a ripple be attributed to another quantity. effect throughout the SI. Legal Metrology involves the technical and Derived quantity Name Symbol SI base unit administrative procedures established by law, Square meter m2 m2 by public authorities to guarantee the quality of Cubic meter m3 m3 measurements. Statutory requirements come Meter per second m/s m · s-1 from: the need to protect health, public safety, N m · kg · s-2 environmental concerns, enabling taxation, con- Pa m-1 · kg · s-2 sumer protection, fair trade and more. Electric resistance Ω m2 · kg · s-3 · A-2 F m2 · kg-1 · s4 · A2 Legal Metrology ensures that we maintain our EMF V m2 · kg · s-3 · A-1 measurement systems. Manufacturers, hospitals Temperature celsuis °C K and, medical facilities have a legal responsibil- ity to keep records to show that medical devices Why does metrology matter? and the test instruments used to calibrate them Metrology is born out of physics and is ubiqui- are accurate and traceable. There are number of tous; it underpins most other technologies to organizations that provide international support some degree. It has three primary and critical for legal metrology, including: subfields: • International Organization of Legal Metrology Scientific or Fundamental Metrology establishes (OIML) quantity systems and the development of new • European Cooperation in Legal Metrology measurement methods and standards. Handled (WELMEC) by the BIPM internationally, Fluke Biomedical, • Asia-Pacific Legal Metrology Forum (APLMF) RaySafe and its distributors also participate through committees established by the national measurement institutes (NMI) Why measurements matter Imagine the chaos if every country and state had The BIPM has several vital committees that a different measurement system. Our economy provide guidance documents for the metrology and our everyday lives rely on consistency and community and have a mission to harmonize trust in the goods we buy and sell. We also ex- worldwide metrological practices and dissemi- pect that the products we use must be capable nate scientific and technological knowledge of operating within their stated minimum perfor- mance standards. • Joint Committee for Guides in Metrology (JCGM) Interoperability is also crucial. In a global econ- – JCGM 100:2008 omy, we need measurements on components (GUM—Evaluation of Measurement Data) manufactured overseas to be as accurate as the – JCGM 200:2012 measurements we perform in the US. The reli- (VIM—International Vocabulary of Metrology) able quality of parts means we can trust that the • Joint Committee for Traceability in Laboratory individual pieces will fit together, physically and Medicine (JCTLM) electrically without effort. Adhering to standards and producing products Applied, Technical or, Industrial metrology is the that match measurement guidelines is a require- application of measurement science to manufac- ment for any manufacturer today. Metrology ac- turing and other industrial processes. It ensures curacy and traceability permeate every aspect of the suitability, and, quality control of the industrial products built.

The pharaohs’ pyramids remind us that metrology has been understood for centuries and it

2 Fluke Biomedical Clinical importance of anesthesia machine testing: A review continues to evolve as devices, calibration and measurements become more and more sophisti- cated.

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