csOc3AtmIntervalCorrectedHEC is a read-only 64-bit counter of the number of ATM cells with a corrected Header Error Control byte, recorded for one specific past 15-minute interval bucket on this OC3 port. Having this broken out by historical bucket lets an admin trace exactly when a signal started getting marginal, rather than only knowing it's currently elevated, helping correlate the onset of degradation with events like a weather event or a fiber-splice job. For example, an admin noticing today's corrected-HEC count is high could scan back through the csOc3AtmIntervalCorrectedHEC buckets to find the exact 15-minute window the errors started, and match it against a maintenance log entry from that time.