Charting Data from Different Worksheets

Here is what I am trying to accomplish but can't seem
to find a way to do it. I have 1 Excel file with 31
different sheets in it (1 for each day of the month)
One of the values on each sheet for example is the #
of Fat grams consumed that day. What I want to do at
the end of the month is to be able to have the total
averages for the month and chart them. For example,
35 Fat grams on average per day in February 2001.
Any Ideas?

Thanks Very Much in Advance!!