I am not getting updates in PivotTable via User Defined Function (UDF) in EWA Web part

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MOSS2007

MS-Excel

SharePoint

I am trying this stuff since 3weeks. Appreciate your help.

My Requirement: Updating PivotTable/Chart whenever Sharepoint List data get change.

My Approach: Applying UDF's in Excel Workbook.

Issue: I am able to get records from my List in my workbook when i run UDF in workbook. Then I Inserted PivotTable based on data fetched from List. I published workbook in trusted location. I enable UDF in trusted location. I can also see PivotTable in my Excel Web Access web part. But, not getting updates in PivotTable/Chart when List data change.

Question: I am confuse that who will run UDF when my workbook seats in trusted location? UDF will run automatically and fetch the data from my Sharepoint List. If so, then my PivotTable should get update?

Guys, Please advice. Appreciate your help.

- Chintan