code: public ReturnValue withPerformanceData(final Metric metric, IThreshold threshold) {
  
          performanceDataList.add(new PerformanceData(metric, threshold.getPrefix(), threshold.getUnitString(), threshold.getRangesAsString(Status.WARNING), threshold.getRangesAsString(Status.CRITICAL)));
          return this;
      }
docs: Adds performance data to the plugin result. Thos data will be added to
  the output formatted as specified in Nagios specifications
  (http://nagiosplug.sourceforge.net/developer-guidelines.html#AEN201)
  
  @param metric
  The metric relative to this result
  @param threshold
  The treshold to be evaluated
  @return this