Microsoft Office Excel 2007 allows to specify different calculation formulas in a workbook.
Once the formula is set up in a workbook and published to sharepoint Excel Services,Excel Calculation setting is supported and retained in the workbook.
To perform the calculation or recalculation:
1. open the appropriate webpart page .
2. Open the workbook in excel web accesss webpart
3. On the webparts toolbar,click the update menu and then click the Calculate workbook
4. Repeat the steps to recalculate