Hello. I'm using Excel 2010.

I'm not much of a spreadsheet designer, so I'm hoping what I want to do is fairly simple.

I want to flag duplicate dates somehow. Here's what I mean:

My spreadsheet has columns for Last Name, First Name, etc. The standard data. One column in particular has dates, formatted like this: 11/14/12.

All I want is for Excel to display a warning or a flag of some sort, if I type in a date that is already in that column. It is not necessary for Excel to inform me which cell has the already-entered date.

So…let's say 03/18/10 is in cell D-10.

If I enter 03/18/10 in oh, let's say cell D-59, I want Excel to inform me somehow that this date has already been entered elsewhere in the same column.

Is this possible? If so, then what is the easiest and most practical way to accomplish this?

If you require further details from me, please let me know.

Thank you very much. J. Danniel