This PerfCounter64 counter reports a count of Severely Errored Seconds, tallied over the most recent completed bin. An admin uses it as a reliability metric distinct from raw error counts, since it reflects how many whole seconds were affected rather than how many individual errors occurred. 38 seconds logged in cmFlowHistorySES for flow 45 in one interval, concentrated in a short burst rather than spread evenly, points an operator toward a single transient event (like a brief optical glitch) rather than steadily degrading hardware.