code: public final double mean(final AbstractMeter meter) {
          checkIfMeterExists(meter);
          final AbstractUnivariateStatistic mean = new Mean();
          final CollectionDoubleCollection doubleColl = new CollectionDoubleCollection(this.meterResults.get(meter));
          return mean.evaluate(doubleColl.toArray(), 0, doubleColl.toArray().length);
      }
docs: Returns the arithmetic mean of the result set. avg() is an alias for this method.
  
  @param meter the meter of the mean
  @return the mean value.