  Busch, Lahti and Werner (BLW) have recently criticized the operator approach
to the description of quantum errors and disturbances. Their criticisms are
justified to the extent that the physical meaning of the operator definitions
has not hitherto been adequately explained. We rectify that omission. We then
examine BLW's criticisms in the light of our analysis. We argue that, although
the approach BLW favour (based on the Wasserstein 2-deviation) has its uses,
there are important physical situations where an operator approach is
preferable. We also discuss the reason why the error-disturbance relation is
still giving rise to controversies almost a century after Heisenberg first
stated his microscope argument. We argue that the source of the difficulties is
the problem of interpretation, which is not so wholly disconnected from
experimental practicalities as is sometimes supposed.
