Double-clicking the metrics to automatically create the graph is really useful. However, when a graph is already open, I find the way it tries to merge the series really unproductive. I frequently get 'Incompatible Series Detected' or 'Additional Metric Can't be Displayed' messages, because as a reflex I want to open the metric without thinking one is already visible.
I think the default behavior should be to always create new graph window. Regardless if a metric is already open or not. Drag and drop works perfectly to merge series.
Perhaps i'm not using it how it was intended...
What do you guys think?