This is how its being used right now:
```
src/naarad/metrics/metric.py:      if self.sub_metric_description and column in self.sub_metric_description.keys():
src/naarad/metrics/metric.py:        graph_title += ' ('+self.sub_metric_description[column]+')'
```
I don't think the way they are defined right now ('raw', 'avg' as keys) help.