csOc3LineDayUASs is a read-only PerfCurrentCount counter reporting the number of Unavailable Seconds — seconds counted once ten consecutive severely errored seconds occur at the Line layer — that the SONET/SDH Line layer of this OC3 port has recorded accumulated so far today. A rising count here is the operational signal that an extended outage of the OC3 line is happening on that interface, which is exactly the kind of degradation a monitoring admin wants an early warning of before it causes an outage. For example, checking csOc3LineDayUASs mid-afternoon and finding it already well above a typical day's baseline is an early sign of an extended outage of the OC3 line on the SONET/SDH Line layer of this OC3 port, well before the day's tally is complete.