Update a cell based on the pivot table refresh date
 

Hello,
I am trying to create an agile burn-down chart in excel 2007. I have a
datafeed to the project database and am creating a pivot table from the
resultant data. I am also able to extract the refresh date from the pivot
table. Here is the issue. I have created two columns from which the chart
will subsequently be created. Column A contains each day's date for the next
30 days. Column B should contain the remaining time-to-completion for the
project for that corresponding day. Taking into account the data and pivot
table will be refreshed daily, how can I update the value in column B from
the pivot table for that date only and prevent further modifications to that
cell? Thanks for any assistance provided.