This counts High Correction Count Seconds -- one-second intervals during the bin where the FEC correction rate on this OTU signal exceeded a defined high-water-mark threshold. Because this reading sits in the rolling window of completed 15-minute history bins for this OTU signal, HCCS is designed as an earlier warning than an outright FEC failure: it flags seconds where the correction engine is working unusually hard on this signal well before the link risks going uncorrectable. For example, an OTU signal that starts logging HCCS occasionally in a bin, even with zero uncorrected FEC blocks, is the kind of signal that justifies scheduling a proactive fiber or amplifier check before the link degrades further, within that completed 15-minute window.