  In this contribution I will review the analysis of the
Einstein-Podolsky-Rosen argument, Bell's inequalities and of associated
experiments for spins in terms of positive operator valued measures.
Specifically, I will explore the relation between the
Clauser-Horne-Shimony-Holt inequality and a fundamental \emph{classicality}
property of observables -- their \emph{coexistence}. A derivation of Bell's
inequalities for unsharp spins will be given which follows a reconstruction by
Mittelstaedt and Stachow of the original EPR argument. In this context we
discuss the need for a consistent relativistic description of localised
measurements, carried out in spacelike separated regions of spacetime on
spatially extended, entangled systems.
