203
the measurand is not necessarily the same as the quantity being measured. On this
matter we have introduced in Sect. 2.3 the distinction between
• the intended property: the measurand, i.e., the property that is intended to be
measured and to which the measurement result is attributed, and
• the effective property: the property of the object under measurement with which
the instrument actually interacts and that causes an effect through the transduction performed by the instrument.
This accounts for the ambiguity of the expressions “measured property” and “property under measurement”, which may refer to both the intended property and the
effective property. This distinction is not maintained in daily measurements, in
which the measurand is often not explicitly defined, because the interest is to measure “here and now” and nothing else, with the goal of obtaining information about
the property that induces the transduction in the instrument.
7
But whenever measurement results are aimed at providing transferable information, such an implicit,
indexical definition is no longer appropriate, and the model of the measurand needs
to be improved, possibly by including in it the specification of values of properties
by which it is affected. In Sect. 3.2 we have called such properties “affecting properties”, because they are the properties that affect the measurand. (Unfortunately the
VIM does not have an entry, nor a term, for this concept.) For example, the length
of an iron rod is affected by temperature, because of thermal expansion, and therefore a measurand could be defined as the length of the rod at a given temperature,
say 293.15 K.
It should be noted that, generally, in a given measurement context the affecting
properties and the influence properties are not the same:
• The affecting properties are causally related to the measurand, and therefore are
in principle independent of the measuring instrument (in the example above the
volume of the rod is modeled in such a way that the temperature of the environment is an affecting property).
• The influence properties are causally related to the transduction implemented in
the measuring instrument, and alter its behavior in producing an indication in
response to a given effective property.
(Of course, a property may be both an affecting property and an influence property:
this does not remove the principled distinction.)
Since affecting properties enter the model of the measurand and influence properties enter the model of the instrument behavior, and since our provisional characterizations of direct measurement and indirect measurement are grounded on the
distinction between these two models, as Table 7.1 highlights, our introduction of
the distinction between affecting properties and influence properties then requires
7 Thus, for example, when measuring the weight of foods at the supermarket, the measurand is
accepted to be the weight of the object put on the scale with no further specifications, though of
course the measuring instrument is expected to be appropriately calibrated, including all relevant
corrections.
7.2 Direct and indirect measurement
the measurand is not necessarily the same as the quantity being measured. On this
matter we have introduced in Sect. 2.3 the distinction between
• the intended property: the measurand, i.e., the property that is intended to be
measured and to which the measurement result is attributed, and
• the effective property: the property of the object under measurement with which
the instrument actually interacts and that causes an effect through the transduction performed by the instrument.
This accounts for the ambiguity of the expressions “measured property” and “property under measurement”, which may refer to both the intended property and the
effective property. This distinction is not maintained in daily measurements, in
which the measurand is often not explicitly defined, because the interest is to measure “here and now” and nothing else, with the goal of obtaining information about
the property that induces the transduction in the instrument.
7
But whenever measurement results are aimed at providing transferable information, such an implicit,
indexical definition is no longer appropriate, and the model of the measurand needs
to be improved, possibly by including in it the specification of values of properties
by which it is affected. In Sect. 3.2 we have called such properties “affecting properties”, because they are the properties that affect the measurand. (Unfortunately the
VIM does not have an entry, nor a term, for this concept.) For example, the length
of an iron rod is affected by temperature, because of thermal expansion, and therefore a measurand could be defined as the length of the rod at a given temperature,
say 293.15 K.
It should be noted that, generally, in a given measurement context the affecting
properties and the influence properties are not the same:
• The affecting properties are causally related to the measurand, and therefore are
in principle independent of the measuring instrument (in the example above the
volume of the rod is modeled in such a way that the temperature of the environment is an affecting property).
• The influence properties are causally related to the transduction implemented in
the measuring instrument, and alter its behavior in producing an indication in
response to a given effective property.
(Of course, a property may be both an affecting property and an influence property:
this does not remove the principled distinction.)
Since affecting properties enter the model of the measurand and influence properties enter the model of the instrument behavior, and since our provisional characterizations of direct measurement and indirect measurement are grounded on the
distinction between these two models, as Table 7.1 highlights, our introduction of
the distinction between affecting properties and influence properties then requires
7 Thus, for example, when measuring the weight of foods at the supermarket, the measurand is
accepted to be the weight of the object put on the scale with no further specifications, though of
course the measuring instrument is expected to be appropriately calibrated, including all relevant
corrections.
7.2 Direct and indirect measurement