TrueSight Capacity Optimization 10.3 is this example but this works with other versions as well.
In this example, we will use CPU a percentage metric, and compare that against CPU RunQueue a count metric. However, this can be done with any two metrics of any two types.
Adapting this slightly, you can change the 'line type' on each of the metrics on a chart, in the "Metric Style" section of the edit screen.
This technique can be combined with other techniques to great effect. I personally like the second Y axis to be a bold blue color and prefer dots instead of lines. Saving your 'favorite' as a template allows for the quick reuse of the design choices made.
Feel free to add your comments and suggestions, and favorite charting design choices.