Hi,

assuming that in workbook Reports month (January, February,...) is in
A1, month day (1-31) is in A2 and part number is in A3, the following
formula should work:

=INDEX(INDIRECT("'[products.xls]"&A1&"!A1:AE20"),MATCH(A3,INDIRECT("'[products.xls]"&A1&"!A1:A20"),0),MATCH(A2,INDIRECT("'[products.xls]"&A1&"!A1:AE1"),0))

We are assuming also that both files are in the same folder.

Does this help?
Kostis Vezerides