= Measured quantity value
A \b[measured quantity value] is a value used to represent a <measurement result>. It may be obtained from one observation or calculated from replicate observations, for example as an <arithmetic mean>. The VIM distinguishes this value from a raw <measurement indication> and from the fuller result with its <measurement uncertainty>.<International vocabulary of metrology by JCGM>[VIM3entry2.10, definition, note1 and annotation9December2016; entry2.9, note2]{ref}
For an original <electrical resistance> example, suppose three instrument indications are $100.04$, $100.06$ and $100.05\,\Omega$. A <measurement calibration> gives additive indication offset $b=0.02\,\Omega$, so the corrected values are $100.02$, $100.04$ and $100.03\,\Omega$. Their <arithmetic mean> is the representative <measured quantity value>
$$
\widehat R=\bar r-b=100.03\,\Omega.
$$
This value is a numerical estimate of the specified <measurand>, such as the resistor's resistance at a stated temperature. It is not established as an exact true value merely by correcting the indications.
The three values have sample <standard deviation> $s=0.01\,\Omega$. If repeat deviations are independent, their contribution to the mean's <standard uncertainty> is $s/\sqrt3\simeq0.0058\,\Omega$. Suppose the common correction has independent <standard uncertainty> $u(b)=0.02\,\Omega$. First-order <propagation of uncertainty> gives
$$
u(\widehat R)=\sqrt{s^2/3+u(b)^2}\simeq0.0208\,\Omega.
$$
Repeating the readings reduces the first term under these assumptions; it does not repeatedly remeasure and average away the same common correction. These are illustrative uncertainty inputs, not observed equipment data.
Reporting the <measured quantity value> therefore requires its unit and <measurand> definition. Reporting the complete <measurement result> also identifies the associated <measurement uncertainty>, its convention and relevant conditions. A change from ohms to milliohms changes the numerical expression, while leaving the represented physical value unchanged.
Back to article page
