If the chart is linked to the cell data then this should happen
automatically.
Check that the chart data is actually range references and not values.
Also make sure the workbook is not is manual calculation. (Try F9)
Another possiblity is that although the values have changed the
proportions haven't. Giving the appreance of no change.
How can I get my pie chart to automatically update after
changing the data on the spreadsheet?
