Hi there;

I'm looking for a way to tally up data that matches certain criteria.
Here's my scenario:
Each object has Given Data:
1) ID Number (B2:B2000 of spreadsheet)
2) Size (L2:L2000; can be S M L XL)
3) Month (D2:D2000 can be 08 or 09)
4) Day (E2:E2000 can be any 01 - 31)

Each ID appears several times with various data associated. I want to
count each ID just ONCE for the conditions:
Dates: August 6 - 12
Size: Medium

I can count every occurrence of the ID by using SUMPRODUCT as follows:
=SUMPRODUCT(--($L$2:$L$2000="M"),--($D$2:$D$2000=8),--($E$2:$E
$1906=6),--($E$2:$E$1906<=12))

How can I include the condition that each ID in column B can only be
counted once?

Many many thanks!