Autoexecute macro to check duplicate entries

[1021557]

Hi,

Is there an easy way to attach a macro that will run when a sheet is open so that if a value is entered say in A10 and the value already exisst in the range A1:A9 then a message warning that it's a duplicate will appear?

Thanks

 

[VoG]

Try this: right click the sheet tab, select View Code and paste in

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Column = 1 Then
    If WorksheetFunction.CountIf(Columns("A"), Target.Value) > 1 Then MsgBox "Duplicate!", vbInformation
End If
End Sub