Hi was wondering if you guys could help me with this.

I am trying to do a simple graph comparing sales month by month of 2001, 2002 and 2003.

So there will be a sales figure of each month from 2001 to 2003

However I would also like to have a secondary axis called TOTAL totalling all 2001-2003 sales (for all months). Because of this figure will significantly be a lot higher, how do I plot this on a Y-axis with a higher axis?