code: public final double sum(final AbstractMeter meter) {
          checkIfMeterExists(meter);
          final AbstractUnivariateStatistic sum = new Sum();
          final CollectionDoubleCollection doubleColl = new CollectionDoubleCollection(this.meterResults.get(meter));
          return sum.evaluate(doubleColl.toArray(), 0, doubleColl.toArray().length);
      }
docs: Computes the sum over all data items.
  
  @param meter the meter of the mean
  @return the sum of all runs.