This read-only Gauge reports the number of Severely Errored Seconds encountered by this DS1 interface in one specific historical 15-minute interval, the completed-interval counterpart to dsx1CurrentSESs. This gives historical visibility into severe (not just minor) error events for a specific past window, useful for distinguishing whether a historical incident involved serious degradation or just minor, tolerable errors. An engineer building a report justifying a hardware replacement would cite a string of past intervals where dsx1IntervalSESs was consistently elevated, showing a pattern of severe degradation rather than an isolated blip.