DLookUp, using value from report as criteria?

[quadomatic]

I'm trying to write an expression to get a value from another table, using a value from a report. Here's my attempt:

=DLookUp("[activity_desc]","[ActivityCode]","[activity_cd] = activity_cd")

I'm trying to get the value from the field "activity_desc" in the table "ActivityCode", where the value of the field "activity_cd" (in the "ActivityCode" table) is equal to the value of "activity_cd" in the report. I'm not really sure how to make that last activity_cd part refer directly to the value of activity_cd in the report.

Any help? I'm normally used to working with PHP and MySQL, but access expressions are like greek to me.

 

[Galaxiom]

"[activity_cd] = Reports!reportname!activity_cd")