  Niels Bohr proposed that the outcome of the measurement becomes objective and
real, and, hence, classical, when its results can be communicated by classical
means. In this work we revisit Bohr's postulate using modern tools from the
quantum information theory. We find a full confirmation of Bohr's idea: if a
measurement device is in a nonclassical state, the measurement results cannot
be communicated perfectly by classical means. In this case some part of
information in the measurement apparatus is lost in the process of
communication: the amount of this lost information turns out to be the quantum
discord. The information loss occurs even when the apparatus is not entangled
with the system of interest. The tools presented in this work allow to
generalize Bohr's postulate: we show that for pure system-apparatus states
quantum communication does not provide any advantage when measurement results
are communicated to more than one recipient. We further demonstrate the
superiority of quantum communication to two recipients on a mixed
system-apparatus state and show that this effect is fundamentally different
from quantum state cloning.
