Something like:

=IF('[workbook1.xls]Sheet1'!A1='[workbook2.xls]Sheet1'!A1,'[workbook2.xls]Sheet1'!B1-'[workbook1.xls]Sheet1'!B1,"")

HTH
JG

"RMD at JMU" wrote:

How do I reference a cell in a different workbook so that I may use it in a
formula?
Ex. If Workbook 1 Column A = Workbook 2 Column A, then subtract Workbook 1
column B from Workbook 2 column B.
--
RMD