  We formulate the dynamics of the generic quantum system S_{c} comprising a
microsystem S and a macroscopic measuring instrument I, whose pointer positions
are represented by orthogonal subspaces of the Hilbert space of its pure
states. These subspaces are simultaneous eigenspaces of a set of coarse grained
intercommuting macroscopic observables and, most crucially, their
dimensionalities are astronomically large, increasing exponentially with the
number, N, of particles comprising I. We formulate conditions under which the
conservative dynamics of S_{c} yields both a reduction of the wave packet
describing the state of S and a one-to-one correspondence, following a
measurement, between the pointer position of I and the resultant eigenstate of
S; and we show that these conditions are fulfilled, up to utterly negligible
corrections that decrease exponentially with N, by the finite version of the
Coleman-Hepp model.
