  Our investigation of the results of the neutron spin experiment by Ehhart et
al. demonstrates that their results cannot be understood in accordance with
common sense. For example, their results obtained with different measurement
errors are equal to each other for a same neutron state. This is because their
measurement values have a large systematic error due to adopting an incorrect
measurement-value operator, which is the operator that gives the measurement
values of the measured observable. They asserted that their results confirmed
the validity of a universally valid uncertainty relation proposed by Ozawa.
Therefore, their results demonstrate unexpectedly that Ozawa's uncertainty
relation holds true for incorrect measurements. In addition, we have proved
this fact theoretically. The measurement-value operator must be defined in
order that the systematic error of measurement values predicted by the operator
is zero. Such a measurement is called an accurate measurement. Two kind of
uncertainty relations are derived for accurate measurements of a
pre-measurement observable $\hat{x}_0$. In addition, we have presented an
uncertainty relation for accurate measurements of a post-measurement observable
$\hat{x}_t$. Heisenberg's original uncertainty relation for measurement
processes should be interpreted as this relation between the resolution, that
is, the measurement error of the post-measurement observable $\hat{x}_t$ and
the disturbance of an object observable $\hat{y}_0$.
