This integer, ranging 1 to 900 seconds, reports how much of the current 15-minute Line-layer error-measurement period has elapsed so far. An admin cares because it provides the denominator for judging how representative the current Line-layer error counters are — near 900 means the interval is essentially complete, while a low value means the counts are still a small partial sample. For example, seeing a jump in cwSonetLineCurrentESs at only 60 seconds into the interval flags a fast-onset problem rather than a slow accumulation.