  We discuss the Full Counting Statistics of non-commuting variables with the
measurement of successive spin counts in non-collinear directions taken as an
example. We show that owing to an irreducible detector back-action, the FCS in
this case may be sensitive to the dynamics of the detectors, and may differ
from the predictions obtained with using a naive version of the Projection
Postulate. We present here a general model of detector dynamics and
path-integral approach to the evaluation of FCS. We concentrate further on a
simple "diffusive" model of the detector dynamics where the FCS can be
evaluated with transfer-matrix method. The resulting probability distribution
of spin counts is characterized by anomalously large higher cumulants and
substantially deviates from Gaussian Statistics.
