This read-only PerfCounter64 reports the sum of squares of backward (R2P) Frame Delay Range samples, in microseconds squared, collected during the current interval, per its description. An administrator's analysis tools use this to compute the variance of return-path delay variation, complementing the equivalent forward-direction statistic. For example, an engineer comparing forward versus backward FDR variance would use this object to determine whether the return path is less stable than the outbound one.