When a property or an existing building at the time of the passage of this title has a use which is legal prior to the passage of this title, such use may continue even though same be not in conformity to the zoning regulations. If, however, the use of the building or premises is changed, it shall be changed to use conforming to the zoning regulations and, after such change, it will not be permissible to change back again to the original nonconforming use. (Ord. 130, 12-29-1975)