13 month rolling chart

Hi,

I have the following data:

July 07 Aug 07 Sept 07 ...................... Jul 08 Aug 08
Series 1 25 30 32 ...................... 42
Series 2 25 27 28 ..................... 32
Series 3 5 7 8 ...................... 10

Series 1 & 2 are bars, series 3 is a line graph, all on the same graph.

My graph currently shows the data for the last year (i.e. 13 months inclusive). Each month I enter new data and have to manually update the graphs by changing the Source Data and dragging it across.

What formula can I enter so that my graphs update as soon as I type in a value to the most recent month?

Currently the Series Names are in Cells B5,B6 and B7 respectively.
The current values in the graph are as follows:
Series 1 I5:U5
Series 2 I6:U6
Series 3 I7:U7

Next month's data will be entered in V5,V6 and V7.

Thanks in advance for your help.

Ed