This counter reports the number of Severely Errored Framing Seconds encountered at the Section layer during one specific historical 15-minute interval in the past 24 hours. An admin cares because SEFS in a past interval means frame synchronization was actually lost during that window, a much more serious historical event than ordinary bit errors, useful for confirming whether a reported brief outage was a hard framing loss. For example, a nonzero SEFS count at a specific past interval combined with customer complaints of a dropped connection around that time confirms a genuine sync loss occurred.