  Quantum experiments usually assume the existence of perfect, classical,
reference frames, which allow for the specification of measurement settings
(e.g. orientation of the Stern Gerlach magnet in spin measurements) with
arbitrary precision. If the reference frames are "bounded" (i.e. quantum
systems themselves, having a finite number of degrees of freedom), only limited
precision can be attained. Using spin coherent states as bounded reference
frames we have found their minimal size needed to violate local realism for
entangled spin systems. For composite systems of spin-1/2 particles reference
frames of very small size are sufficient for the violation; however, to see
this violation for macroscopic entangled spins, the size of the reference frame
must be at least quadratically larger than that of the spins. Unavailability of
such reference frames gives a possible explanation for the non-observance of
violation of local realism in everyday experience.
