Is there a way to detect duplicate dates as I enter them?

[Karin]

Hi. I need to take an inventory of over 4,000 film can that we have in our vault. First I need to go though get basic information from each can. I created a simple spreadsheet in numbers to track this information. We are tracking these cans by the date on the side of each one. Most of these dates are unique, but there may be some duplicates. What I need is some way for the spreadsheet to alert me to the fact that I am entering a duplicate date when I enter it so I can add an additional indicator to the date. This way I won't have two cans with the same title. Is there a way for Excel to detect duplicate information as I enter it? I had hoped that the autocomplete function might do it, but this only works in adjacent cells.



-Karin