You can use the Choose function to create a calculated control whose value is determined by the value of a field in a table in your database. For example, suppose you have a Shippers table that contains a field called ShipperID. You could create a calculated control on a form to display a text name for the shipper based on the value of the ShipperID field.
=Choose([ShipperID], "Speedy", "United", "Federal")