This read-only PerfCounter64 is the historical counterpart to f3EsaProbeStatsSoamPmExtSumOfSqAbsRTJitter, recording the sum of squares of jitter samples for a completed, archived interval. An administrator's analysis tools use this to recompute the historical jitter variance or standard deviation for a past interval, revealing how bursty jitter was rather than just its average. For example, an engineer comparing archived intervals before and after a network change would use this figure to see if jitter became more or less consistent.