csOc3AtmCurrentUnCorrectedHEC is a read-only 64-bit counter of the number of ATM cells on this OC3 port whose Header Error Control byte had errors too severe to correct, meaning those cells were discarded. Unlike the corrected-HEC counter, any nonzero value here represents actual cell loss the receiving equipment could not recover from, making it a much more urgent signal of a degraded or failing optical path. For example, an admin seeing csOc3AtmCurrentUnCorrectedHEC start incrementing, especially alongside a rising csOc3AtmCurrentCorrectedHEC trend, would treat it as confirmation that the marginal signal has crossed into causing real, unrecoverable cell loss and escalate accordingly.