To build up formulas using values from several different workbooks, just
think of them all as one multi-chapter mega-workbook. So instead of having a
formula such as
=A1 + B1
where you get values from the same sheet, or a formula like
='Sheet 4'!V9 / 'Sheet 12'!X44
to use two values on different sheets within the same workbook, you just
need to go one step further and provide the workbook name(s) involved. Such
a formula might look a little like this:
='[Book One]Sheet 5'!$B$5 + '[Book Two]Sheet 7'!$R$22 - '[Book 14]Sheet3'!$A$2
You can get Excel to do most of the work for you:
Have all concerned workbooks open at once, then go to the place you need the
multi-book formula and start a formula by typing in the = symbol, then
activate one of the other books, choose the proper sheet in it, and the
needed cell in it.
To continue a formula just press the key you need such as + - / * () or
start typing a function name, then when it comes time to get another value
from some other book, once again choose the workbook, worksheet in it, and
cell on that sheet and continue until you are done. When you are finished
building the formula, press the [Enter] key to end it all and finalize it in
your workbook.

There are a few worksheet functions that do not work while the other
workbooks are not open - you won't run into them often. Just be aware that
if you have built up some formula that looked great while all the workbooks
were open but suddenly have error indications in them, you may have hit one
of those functions. Try opening all involved workbooks to see if the errors
don't clear.

Also, in the formulas I used above, when you close those other workbooks,
the references to the workbook names are going to change to complete paths
with the workbook names. And they still work. However, if you take the file
to another machine somewhere without the same folder structure and without
access to those other files, then you will have links problems - you'll
probably get a prompt as to whether to change the links, update their values
or not, and you can elect to simply keep the last values obtained. Another
option would be to use the Edit | Links option to point them to the proper
files if they are available at all. Just something else to be aware of. If
the files all reside on a single computer where the path to them won't
change, or if they are available on a network and the network path has been
used to specify them, then this problem doesn't even rear its ugly head.

"yakdog" wrote:

Excel 2003. I have three works with data in them and would like to summarize
the data in a fourth workbook. I know how to link two workbooks together, but
not how to link multiple workbooks together.