What does measurement uncertainty actually mean? And what lies behind terms such as traceability, metrology and measurement result?
At the Norwegian Metrology Service (Justervesenet), we work every day to ensure that measurements in Norway are reliable and traceable to international standards. Here you will find our explanations of many of the terms used in metrology.
These are not official definitions as described in ISO standards.
Accreditation is an official recognition that demonstrates an organisation’s competence to perform specific tasks according to established requirements. These requirements are set out in laws, regulations or standards.
Accreditation is granted by an accreditation body, such as Norwegian Accreditation.
The Norwegian Metrology Service is accredited to perform conformity assessments as a Notified Body for the following measuring instruments (directives and conformity assessment modules in parentheses):
• Automatic weighing instruments (MID, Modules B, D, F, G)
• Flow meters for liquids (MID, Modules B, D, F, G)
• Electricity meters (MID, Modules B, D, F)
• Multidimensional measuring instruments (MID, Modules B, D, F)
• Non-automatic weighing instruments (NAWID, Modules B, D, F, G)
• Water meters (MID, Modules B, D, F)
• Heat meters (MID, Modules B, D, F)
The International Bureau of Weights and Measures (BIPM) is the international metrology organization established under the Metre Convention. Through BIPM, member states collaborate on matters related to measurement science and measurement standards, particularly the development and maintenance of the International System of Units (SI). BIPM is located in Sèvres, just outside Paris, France.
The CE marking is the manufacturer’s declaration that a product complies with the requirements of the relevant EU/EEA legislation. The marking is used on a wide range of product groups, not only measuring instruments.
For measuring instruments covered by the Measuring Instruments Directive (MID) or the Non-Automatic Weighing Instruments Directive (NAWID), the CE marking must be used together with the M marking. Together, these markings indicate that the instrument has undergone the required conformity assessment and may be placed on the market within the EU and EEA.
A coverage factor (k-factor) is a numerical factor used to calculate measurement uncertainty. The factor determines the size of the interval around a measurement result and, consequently, the probability that the true value lies within that interval.
For k = 1, the probability is approximately 68%, and for k = 2, the probability is approximately 95%, assuming that the measurement result follows a normal distribution.
A deviation is the difference between a measured value and the true value. In metrology, the term is used for results that do not correspond to a reference value or that fail to meet requirements specified in regulations, standards, contracts, or quality management systems.
Deviation is calculated as:
Deviation = measured value − true value
The true value is normally established using reference equipment that has been corrected for all known errors and influencing factors.
In the field of measurements, a user is, in practice, a person or a company registered in the Central Coordinating Register for Legal Entities (Enhetsregisteret) that is responsible for, and owns or has the right to use, the measuring instrument. The user is also responsible for ensuring that the measurement is carried out.
