  The present paper is a sequel to papers dealing with recent developments on
the issue of `quantum measurement'. In this paper `measurement within the
domain of application of quantum mechanics' is treated as a \emph{quantum
mechanical} \emph{interaction} of a `(sub)microscopic object $(o)$' and an
`equally (sub)microscopic part of the measuring instrument $(a)$ being
sensitive to the (sub)microscopic information', that interaction to be
described by a Schr\"odinger equation. The Stern-Gerlach experiment is used as
a paradigmatic example. An alternative to the Heisenberg inequality is found,
exhibiting the \emph{independent} contributions of `preparation of the initial
state of object $(o)$' \emph{and} `interaction of object $(o)$ \emph{and}
measuring instrument/probe $(a)$'. Applicability of the Liouville-von Neumann
equation is stressed.
