8.4 Error Versus Measurement Uncertainty
123
The measurement uncertainty determines the predictable limits of the variability of errors that could not be compensated for or eliminated.
8.5 Errors in Measurements of Chemical Quantities
A very important step of all the studies of the natural phenomena is the determination
of the properties of a given substance (e.g., the chemical composition of water),
mainly by performing measurements. In scientific research, observations are made
through the measurements of the selected, characteristic quantity (e.g., the content
of cadmium in water) and calculating its numerical value, expressed with the use of
selected units (see Chap. 3). As practice shows, when performing the measurement
of the same quantity multiple times, even with the utmost care, we always obtain
a set of different numerical values. Those differences stem from the influence of
various factors on the measuring process. It is, therefore, justified to query how
the result of the measurement can be shown so that it reflects the true value to
the best possible extent. It is also justified to query how confident we are of the
obtained value. The science of measurement (metrology) defines the terms random,
systematic, gross error and measurement uncertainty. In the natural sciences, error
is not, however, a synonym of mistake. As highlighted previously, the measurement
error is the difference between the measurement result and the true value of the
measured quantity. The measurement error means an impossible to avoid uncertainty,
inseparably connected with the essence of each measurement of physical (length,
mass, time) or chemical (the content of the given component) quantities. The role of
the analyst is to estimate its value and to make the uncertainty as small as possible.
When introducing the term ‘error,’ in accordance with the error theory, the true
value of the measured quantity (the object property) is recalled. It is known that in
practice we do not know the true value and we can only refer to a value that is the
best possible approximation of the true value. Therefore, in the VIM 3 dictionary,
the term ‘the correctness of the measurement’ was introduced, which refers to the
reference value. On the other hand, the definition of the measurement error includes
the comparison of the measured value and the reference value. In the comments on
the definition (Clause 2.16, VIM 3), it is highlighted that the reference value can
come from the measuring standard or be an agreed value of the true value. It follows
that in practice we depart from using the term ‘true value’ in the definitive meaning,
since the use of the term ‘reference value’ is more justified.
123
The measurement uncertainty determines the predictable limits of the variability of errors that could not be compensated for or eliminated.
8.5 Errors in Measurements of Chemical Quantities
A very important step of all the studies of the natural phenomena is the determination
of the properties of a given substance (e.g., the chemical composition of water),
mainly by performing measurements. In scientific research, observations are made
through the measurements of the selected, characteristic quantity (e.g., the content
of cadmium in water) and calculating its numerical value, expressed with the use of
selected units (see Chap. 3). As practice shows, when performing the measurement
of the same quantity multiple times, even with the utmost care, we always obtain
a set of different numerical values. Those differences stem from the influence of
various factors on the measuring process. It is, therefore, justified to query how
the result of the measurement can be shown so that it reflects the true value to
the best possible extent. It is also justified to query how confident we are of the
obtained value. The science of measurement (metrology) defines the terms random,
systematic, gross error and measurement uncertainty. In the natural sciences, error
is not, however, a synonym of mistake. As highlighted previously, the measurement
error is the difference between the measurement result and the true value of the
measured quantity. The measurement error means an impossible to avoid uncertainty,
inseparably connected with the essence of each measurement of physical (length,
mass, time) or chemical (the content of the given component) quantities. The role of
the analyst is to estimate its value and to make the uncertainty as small as possible.
When introducing the term ‘error,’ in accordance with the error theory, the true
value of the measured quantity (the object property) is recalled. It is known that in
practice we do not know the true value and we can only refer to a value that is the
best possible approximation of the true value. Therefore, in the VIM 3 dictionary,
the term ‘the correctness of the measurement’ was introduced, which refers to the
reference value. On the other hand, the definition of the measurement error includes
the comparison of the measured value and the reference value. In the comments on
the definition (Clause 2.16, VIM 3), it is highlighted that the reference value can
come from the measuring standard or be an agreed value of the true value. It follows
that in practice we depart from using the term ‘true value’ in the definitive meaning,
since the use of the term ‘reference value’ is more justified.