  In its original formulation, Heisenberg's uncertainty principle dealt with
the relationship between the error of a quantum measurement and the thereby
induced disturbance on the measured object. Meanwhile, Heisenberg's heuristic
arguments have turned out to be correct only for special cases. A new
universally valid relation was derived by Ozawa in 2003. Here, we demonstrate
that Ozawa's predictions hold for projective neutron-spin measurements. The
experimental inaccessibility of error and disturbance claimed elsewhere has
been overcome using a tomographic method. By a systematic variation of
experimental parameters in the entire configuration space, the physical
behavior of error and disturbance for projective spin-1/2 measurements is
illustrated comprehensively. The violation of Heisenberg's original relation,
as well as, the validity of Ozawa's relation become manifest. In addition, our
results conclude that the widespread assumption of a reciprocal relation
between error and disturbance is not valid in general.
