  On the basis of an analysis of previous research, we present a generalized
approach for measuring the difference of plans with an exemplary application to
machine scheduling. Our work is motivated by the need for such measures, which
are used in dynamic scheduling and planning situations. In this context,
quantitative approaches are needed for the assessment of the robustness and
stability of schedules. Obviously, any `robustness' or `stability' of plans has
to be defined w. r. t. the particular situation and the requirements of the
human decision maker. Besides the proposition of an instability measure, we
therefore discuss possibilities of obtaining meaningful information from the
decision maker for the implementation of the introduced approach.
