Abstract: Careful analysis of cluster separability opens a way to a completely new understanding of preparation and registration procedures for microsystems: they are changes of separation status. An important observation is that quantum mechanics does not specify what happens to systems when they change their separation status. New rules that close this gap can therefore be added without disturbing the logic of quantum mechanics. Another important observation is that registration apparatuses for microsystems must contain detectors and that their readings are signals from detectors. This leads to further restrictions on measurability of observables, especially for macroscopic quantum systems. Beltrametti-Cassinelli-Lahti model is used to show how this approach leads to solution of the measurement problem.