8 Measurement Uncertainty
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Due to the complexity of the process of evaluating the measurement accuracy, different evaluation procedures were proposed by experts. In order to limit that diversity
and to unify the process of the evaluation of measurement uncertainty, the International Bureau of Weights and Measures, with inspiration from the International
Committee for Weights and Measures (CIPM) has undertaken actions that resulted
in the publishing of a guide, ISO GUM Guide to the Expression of Uncertainty in
Measurements, in which a uniform process of conduct was proposed when estimating the measurement uncertainty. An important document, in which various advice
on the evaluation of uncertainty in analytical measurements can be found, is the
guide issued by the Eurachem Quantifying Uncertainty in Analytical Measurement.
Currently, the third issue of EURACHEM/CITAC Guide CG 4 (2012) is available.
The term ‘measurement uncertainty’ was accepted by international bodies and is
currently commonly used for the description of the range of probability. It should be
highlighted, however, that the term ‘uncertainty’ can have two meanings: colloquially, to express general doubts regarding measurement results; and in metrological
meaning as a parameter determining the variability of the measurement results within
a defined range. In the metrological meaning, the measurement uncertainty characterizes the justified spread of the value of the measured quantity and it should be
determined for each measurement.
It is worth highlighting that the client—that is, the person interested in the measurement result—does not have to delve into the complexities of the evaluation of
the analytical parameters of the measuring procedures used by the laboratory, but
rather more into the process of evaluation of the quality of the results through the
expression of the measurement uncertainty. Because of that, the efforts of the International Committee for Weights and Measures in the direction of establishing a uniform
method of calculating and providing uncertainty are incredibly important and enable
the comparison of results obtained in different laboratories.
It is worth mentioning here that in ISO 9000 standards, the following sentence
concerning quality management systems in different contexts can be found: “measurement uncertainty is known and in accordance with the required measuring capacity.”. Hence, everywhere that conducted measurements are subject to a measuring
system, the required measurement capacity needs to be defined, and the obtained
results must have an assigned measurement uncertainty. This especially applies to
accredited laboratories.
8.1 Measurement and Its Uncertainty
The term ‘measurement’ encompasses a set of operations aimed at determining the
value of a quantity. It means that there are a set of activities after which we can say
that, at the moment of measurement conducted in specific conditions and after performing specified actions, the measured quantity X is within the specified range of
values. This definition has an unquestionable axiom—that the value of the measurement has the form of a range on the dimensional axis. Thus, the issue is to determine
117
Due to the complexity of the process of evaluating the measurement accuracy, different evaluation procedures were proposed by experts. In order to limit that diversity
and to unify the process of the evaluation of measurement uncertainty, the International Bureau of Weights and Measures, with inspiration from the International
Committee for Weights and Measures (CIPM) has undertaken actions that resulted
in the publishing of a guide, ISO GUM Guide to the Expression of Uncertainty in
Measurements, in which a uniform process of conduct was proposed when estimating the measurement uncertainty. An important document, in which various advice
on the evaluation of uncertainty in analytical measurements can be found, is the
guide issued by the Eurachem Quantifying Uncertainty in Analytical Measurement.
Currently, the third issue of EURACHEM/CITAC Guide CG 4 (2012) is available.
The term ‘measurement uncertainty’ was accepted by international bodies and is
currently commonly used for the description of the range of probability. It should be
highlighted, however, that the term ‘uncertainty’ can have two meanings: colloquially, to express general doubts regarding measurement results; and in metrological
meaning as a parameter determining the variability of the measurement results within
a defined range. In the metrological meaning, the measurement uncertainty characterizes the justified spread of the value of the measured quantity and it should be
determined for each measurement.
It is worth highlighting that the client—that is, the person interested in the measurement result—does not have to delve into the complexities of the evaluation of
the analytical parameters of the measuring procedures used by the laboratory, but
rather more into the process of evaluation of the quality of the results through the
expression of the measurement uncertainty. Because of that, the efforts of the International Committee for Weights and Measures in the direction of establishing a uniform
method of calculating and providing uncertainty are incredibly important and enable
the comparison of results obtained in different laboratories.
It is worth mentioning here that in ISO 9000 standards, the following sentence
concerning quality management systems in different contexts can be found: “measurement uncertainty is known and in accordance with the required measuring capacity.”. Hence, everywhere that conducted measurements are subject to a measuring
system, the required measurement capacity needs to be defined, and the obtained
results must have an assigned measurement uncertainty. This especially applies to
accredited laboratories.
8.1 Measurement and Its Uncertainty
The term ‘measurement’ encompasses a set of operations aimed at determining the
value of a quantity. It means that there are a set of activities after which we can say
that, at the moment of measurement conducted in specific conditions and after performing specified actions, the measured quantity X is within the specified range of
values. This definition has an unquestionable axiom—that the value of the measurement has the form of a range on the dimensional axis. Thus, the issue is to determine