Solved: compare value of two cells to value of two columns in dynamic array

[thole]

I do not even know where to start on this one.
I have an input sheet with 2 columns; 1 of the columns contains unchanging product codes, and the other contains made-up, project-specific codes.
I also have a separate sheet where I have kept all of these codes as entered.
What I would like is to prevent the user to assign the same made-up code to different product codes.
Is this possible?

[rory]

I think you could do this with data validation, or with a Worksheet_Change event, but it would be helpful to see a sample if possible. Would the users be entering the same product/project code combinations more than once? If not, a simple COUNTIF formula would work for the data validation.

[thole]

Thanks, I can see now how to create a list; I think you've pointed me on the right track.