Graph two line same summary field - different find request
I have one table with several records with some summary fields, and the records some are from the year 2012 and some 2013.
I'm able to make a report with total values for each month of a year (summary) and draw a graph with the months in the X axys, and the value in the Y axys for one of the years (2012 for instance).
What I would like to do, is to add to the graph a second line for the 2013 months in the same graph.
How can I do it?