code: @Override
      public double getStdDev() {
          // two-pass algorithm for variance, avoids numeric overflow
  
          if (values.length <= 1) {
              return 0;
          }
  
          final double mean = getMean();
          double sum = 0;
  
          for (long value : values) {
              final double diff = value - mean;
              sum += diff * diff;
          }
  
          final double variance = sum / (values.length - 1);
          return Math.sqrt(variance);
      }
docs: Returns the standard deviation of the values in the snapshot.
  
  @return the standard deviation value