This read-only PerfCounter64 reports the sum of squares of the absolute round-trip jitter samples, in microseconds squared, collected during the current measurement interval, per its description. An administrator's analysis tools use this together with the sum and sample count to compute the standard deviation of jitter, revealing how spread out (bursty) the jitter samples were, not just their average. For example, two intervals with the same average jitter but very different f3EsaProbeStatsSoamPmExtSumOfSqAbsRTJitter values would indicate very different jitter consistency, one steady and one bursty.