esaProbeHistorySumNegR2PJitter is a 64-bit performance counter that reports the running total (sum) of the negative one-way jitter (packet-to-packet delay variation), in microseconds, from the reflector back to the probe, for a completed interval that has already closed and been archived into the rolling history log. Negative (a packet arriving earlier than the one before it) jitter from the reflector back to the probe is exactly the kind of packet-to-packet delay variation that causes stutter in voice and video traffic riding over the same service. For example, re-deriving the average negative jitter from the reflector back to the probe from this archived running total and the matching archived packet count lets an auditor validate the device's own math well after the fact.