esaProbeHistoryAvgRoundTripDelay is an unsigned 32-bit value that reports the average round-trip delay of the test packets, in microseconds, with the reflector's own processing time excluded, for a completed interval that has already closed and been archived into the rolling history log. Round-trip delay is the core proof-of-performance number for an Etherjack SLA test because it reflects everything affecting the circuit in both directions combined, so a technician watches it to confirm the customer's contracted latency bound is being met. For example, graphing this average round-trip delay across several archived bins can reveal a slow, week-over-week degradation trend that no single live reading would ever show.