Prevent Duplicate Entries with Excel Data Validation
You can use Excel's Data Validation tool to prevent a data entry clerk from entering a duplicate account number in a range of cells. In the Data Validation dialog box, use the =COUNTIF() Function. I also show you how to use Paste Special to extend validation to additional cells on your worksheet.
This is one of "The 50 Best Tips for Excel 2007" that I offer on my DVD. I invite you to visit my website - www.thecompanyrocks.com - to learn more about the resources that I offer.