This writable value sets the severely-errored-seconds (SES) threshold for the current 15-minute SONET path interval, above which an alarm fires, and it applies equally to near-end and far-end SES counts. Because SES indicates seconds with a much higher error density than a plain errored second, this threshold lets an admin catch serious, fast-developing path degradation within a quarter hour. For example, a network engineer might tighten this threshold on a leased SONET circuit so that a burst of severely errored seconds during a storm is flagged almost immediately.