Forcing Input from a user
 

If cell A1 is less than 80% how can I force the user to enter information
somewhere else and not be able to continue on, however keeping the value they
have entered into the cell.

i.e.
A1 = 75%, user must type in an "Action Plan on increasing the 70%", Keep
the 75% in cell A1 so we can reference it later.

Best way to create a limited character text field/box/location/sheet/other
suggestion?

Thank you,
Tracy