  In Heisenberg's error-disturbance relation for electron position measurement,
the measurement error must be the one that determines the uncertainty in the
electron position just after the measurement. It is the resolution
$\epsilon(x_t)$ i.e., the measurement error of the post-measurement observable
$\hat{x}_t$, not the precision $\epsilon(x_0)$ i.e., that of the
pre-measurement observable $\hat{x}_0$ that determines the uncertainty of the
observable $\hat{x}_t$. Therefore, Heisenberg's relation must be interpreted as
one between the resolution $\epsilon(x_t)$ and the disturbance $\eta(y_0)$. The
magnitude of the disturbance $\eta(y_0)$ is independent of the definition of
the measurement value of the observable $\hat{x}_t$. Heisenberg's
error-disturbance relation is proven to hold true in general, when the
measurement value of $\hat{x}_t$ is defined in order to minimize the resolution
$\epsilon(x_t)$.
