  In [1], Busch et al. showed that it is possible to construct an
error-disturbance relation having the same form as Heisenberg's original
heuristic definition[2], in contrast to the theory proposed by Ozawa[3] which
we and others recently confirmed experimentally[4,5]. With Ozawa's definitions
of measurement error and disturbance, a relation of Heisenberg's form is not in
general valid, and a new error-disturbance relationship can be derived. Here we
explain the different physical significance of the two definitions, and suggest
that Ozawa's definition better corresponds to the usual understanding of the
disturbance that Heisenberg discussed.
