When using the lookup function in Excel 2003, it would be extremely helpful
to have an error appear if the looked up item does not appear in the list.
Example: If I have a small list of students in list A and I'm trying to look
up the corresponding teacher in list B, it returns a teacher for every
student in list A, even if that student is not in list B, and therefore, it
is the wrong information. I would rather have it display an error message,
so that I know that something is missing.