 In comparison of the two, there are a few positive remarks to make about the Busch-Lahti-Werner (BLW) approach. First of all, by focusing on the distance  (33)  this approach is comparing entire probability distributions rather than just the expectations of operator differences. When this distance is very small, one is justified to conclude that the distribution has changed very little under the measurement procedure. This brings us closer to the conclusion that the error or disturbance introduced is small. Secondly, by introducing a supremum over all states to obtain \(\Delta( Q, Q')\), it follows that when this latter expression is small, the measured distribution \(\mu'\) differs only little from the exact distribution \(\mu\) whatever the state of the system is. As the authors argue, this means that \(\Delta(Q,Q')\) can be seen as a figure-of-merit of the measurement device alone, and in this sense analogous to the resolving power of a microscope.