This holds the sum of the squares of all RTT values received during this ping test, a statistical intermediate value that a management application can use to calculate standard deviation of the path's latency. Admins' monitoring tools use this alongside the average RTT and response count to derive a standard deviation figure rather than relying on min/max alone for variability. A non-zero rbnPingHistoryRttSumOfSquares value feeds directly into a monitoring tool's standard-deviation calculation for that test's latency data.