This read-only PerfCounter64 reports the sum of squares of round-trip Frame Delay Range samples, in microseconds squared, collected during the current interval, per its description. An administrator's analysis tools use this with the sum and count to compute the standard deviation of round-trip delay variation, indicating consistency rather than just an average. For example, an engineer benchmarking a new path would use this figure to determine whether round-trip delay variation is trending more or less consistent over successive intervals.