  In the Copenhagen interpretation the Heisenberg uncertainty relation is
interpreted as the mathematical expression of the concept of complementarity,
quantifying the mutual disturbance necessarily taking place in a simultaneous
or joint measurement of incompatible observables. This interpretation has
already been criticized by Ballentine a long time ago, and has recently been
challenged in an experimental way. These criticisms can be substantiated by
using the generalized formalism of positive operator-valued measures, from
which a new inequality can be derived, precisely illustrating the Copenhagen
concept of complementarity. The different roles of preparation and measurement
in creating uncertainty in quantum mechanics are discussed.
