chart/graph - creation data series

[ajm]

I am trying to build a chart that will let my users select a particular account manager and then a customer group to display that combination's weekly results for last year. I have the account managers listed in validation list. Each account managers name is also the name of a named range (without any spaces) holding those companies for which they are responsible. I have currently got a worksheet change event to change the underlying data (in a pivot table) according to the selections made. How do i now get the weekly data to populate the data series for the actual chart? do i need to create a named range for each of the customer groups? there are several hundred so i am hoping there might be a better solution...