You may consider a third option, conditional formating. Data validation will
prevent the data to be entered, while conditional formating will allow the
data entered, but show a warning (like red fill, for example)
In both cases you can use formulas that evaluate to TRUE or FALSE, with the
"Custom" criteria in Data validation, and the "Formula Is" in conditional
formating.

Hope this helps,
Miguel.

"maryj" wrote:

Users will enter in Column B the order date. In Column C they will enter the
expected ship date. If the expected ship date is less than 8 weeks (not
including weekends), I would like a message to pop up. I'm using the formula
=IF(B7="","",INT((C7-MOD(C7-O7,7)-B7+7)/7)) (O7 contains the value indicating
that Sunday is the first day of the week). Is this possible with data
validation or do I need to use a message box? If I need a message box, I am
not very proficient in VBA so would need some guidance on that. Thanks so
much!
--
maryj