We can now do this as part of the Spring 17 Release out of the box:**
A question I get asked a lot is how we can place multiple measures on a single time series graph in Analytics cloud. This can be achieved really quickly in SAQL / PIGQL.
The idea here is to project each measure for each line on the graph then add an extra column to the projection essentialy for grouping the graph. Once we have both of our measures projected we then union these projection sets to combine them.
Now to plot these , in the appropriate compact form we add both the timeseries groupings and the projected column, usually we name this something like type.
This is shown in the below example, a quick tip here is that Sales Wave has a large number of these examples so you can pop into the code and see these in a working state.
The Specific step JSON / SAQL:
I have also included the full dashboard example for review: