Embodiments of the present invention relate generally to a monitoring unit and method which counts a number of qualified clusters of a selected event type based on a size threshold, granularity threshold, and distance threshold time. In one embodiment, a qualified cluster is a cluster which meets both the size threshold and granularity threshold. In one embodiment, a qualified cluster is detected and counted by the cluster counter if it occurs at least the distance threshold time after a previous counted qualified cluster. For example, in one implementation, the performance monitor waits until a distance threshold time expires prior to detecting a next qualified cluster. Alternatively, all qualified clusters are detected where the cluster counter counts a qualified cluster only if it occurs at least the distance threshold time after a previous qualified cluster, regardless of whether it was counted by the cluster counter or not.