This read-only IetfYangTypesDateAndTime value records when the performance-monitoring counters at the physical-port level were last cleared, defaulting to the all-zero timestamp. It gives operators the time window that a port's counters (like errored seconds or Tx/Rx byte counts) actually cover, which is essential before comparing counts across ports or over time. For example, an operator comparing error rates on two ports should first confirm both have the same portStatisticsEntryLastClear time so the comparison covers an equal monitoring interval.