hello,
I would like to do a formula in one box there is a drop-down of all the
states. Some of the states we have specific data for, so if that state is
chosen, then the customer inputs an area code in the next box. I want to be
able to check that area code to a list of area codes on another sheet. How
would I be able to do this?

Example:

Step 1: A state is chosen: Texas (assume this state is one where additional
data is needed, if no additional data is needed then Step 2 doesn't happen,
and automatically get "OK")

Step 2: Blank (Are code is put in...so let's say 972)
Step 3: A check is done...so that if this area code is in the list "OK",
otherwise, "Error"