esaProbeStatsSumNegR2PJitter 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 the interval that is still being actively collected (the live bin). 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, the technician can divide this live running total by the packet count reported in the same still-open bin to independently recompute the average negative jitter from the reflector back to the probe before the bin rolls over.