code: public double getDistance() {
          if (mDistance == null) {
              double bestRssiAvailable = mRssi;
              if (mRunningAverageRssi != null) {
                  bestRssiAvailable = mRunningAverageRssi;
              }
              else {
                  LogManager.d(TAG, "Not using running average RSSI because it is null");
              }
              mDistance = calculateDistance(mTxPower, bestRssiAvailable);
          }
          return mDistance;
      }
docs: Provides a calculated estimate of the distance to the beacon based on a running average of
  the RSSI and the transmitted power calibration value included in the beacon advertisement.
  This value is specific to the type of Android device receiving the transmission.
  
  @see #mDistance
  @return distance