How about using an auto-enter calculation on the Department field with a case() statement referencing the code field?
Code = 10 ; "QC" ;
Code = 20 ; "QA" ;
Code = 30 ; "QA" ;
You can even uncheck the "do not replace existing value" checkbox for the field so that it updates anytime a new code is selected.
Besides hardcoding with a case statement, you could create a small auxiliary table with just 2 fields, code and department.
You can then autoenter the Department via lookup or via ExecuteSQL (which makes defining a relationship useless), preparing the road for future code & department associations.
Thanks Mike, It works.