Drop down list validation

[vasilis999]

Good morning from Greece! I'm new in our forum and a beginner in excel. And i have problem with a drop list.
I try to make a invoice form whith excel 2007, my country version. In the first sheet
i make a drop down list(about 20 cells) whith the data from another sheet. And i wish that every time
i choose an item from the list that i previously use, to receive a warning message whith the
duplicate entry. I have no problem to make this entry, even duplicate, but i must now that i choose
many times the same subject.
I have submit below an example.
Μy apologies for my english!

[Fotis1991]

Hi there-Καλημέρα Βασίλη!

As you say that you are new to Excel i suggest you to learn firstly the basics about formulas and then to use VBA.

For your query i suggest a Conditional formatting, using this simple formula to highlight all duplicate choices in validation lists.

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How can you use Conditional Formating.

--In Excel 2007 and 2010, Conditional Formatting is in the Styles group on the Home tab. In Excel 2003, Conditional Formatting is on the Format menu. See here how you can work using CF.