Simple question but maybe not a simple answer. I have a graph of performance results by employee expressed as a %. I can express these results aggregated up from employee, to manager, to director, to VP on single views.
A director has asked if he could see his results shown against the aggregated performance of his boss. Ie: a single Director and his VP result on the same graph so he can see how he's doing against his peers. This requires two levels of aggregation to coexist on the same report, which is not a trivial requirement.