  An apparatus model with discrete momentum space suitable for the exact
solution of the problem is considered. The special Hamiltonian of its
interaction with the object system under consideration is chosen. In this
simple case it is easy to illustrate how difficulties in constructing the
dynamical interpretation of selective collapse could be overcomed without any
limiting procedure. For this purpose one can apply either averaging with
respect to a non-quantum parameter or reducing the algebra of the joint system
operators (i. e. passing to the quantum system subalgebra). The latter
procedure effectively implies averaging with respect to apparatus quantum
variables not belonging to the system.
