Moving the closing Stock to Opening stock

[Betty]

I am running Access 97. I have one main report that is
made up of Opening Stock, Data from different subreports
and Closing stock. This Information is for several
products. The formular for the Closing stock is on the
last row of the Main Report. How can I get the closing
stock for today to be the opening stock for the next
day,all the products. The report is run based on dates.
Thank