Description: The interval during which the measurements are accumlated. Interval index 1 indicates the latest interval for which statistics accumulation is completed. Older the statistics, greater the interval index value. In a system supporting a history of n intervals with interval count 1 and interval count n, the most and the least recent intervals respectively, the following apply at the end of an interval: - statistics for interval count n are discarded - the statistics for interval count i become statistics for interval count i + 1, where 1 <= i < n - current statistics become statistics for interval count 1.