This read-only PerfCounter64 counts the number of delta_ts in the probe-to-reflector direction during which the FLR exceeded the configured availability threshold, per its description. An administrator monitors this to quantify how many measurement sub-intervals were bad enough to threaten availability in that direction specifically. For example, a rising count here while the R2P equivalent stays flat would tell an operator the problem is one-directional, likely on the outbound path from the probe.