I'm sorry that I don't understand the context. Maybe "cell" is not
properly defined. Using ThisWorkbook and the change event, the
following code does the simple test and outputs a message--nothing
more.

Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As
Range)
If Mid(Target.Value, Len(Target.Value) - 2, 1) < "." Then MsgBox
"Invalid"
End Sub

HTH,