30. No weight or measure shall be sold, delivered or in any manner used as a commercial weight or measure unless the description of the weight or measure which it purports to be is marked on it in the prescribed manner: Provided that where, in the case of any commercial weight or measure or any class thereof compliance with the requirement of this section is not, in the opinion of the Government, practicable, the Government may, by notification in the official Gazette, exempt such weight or measure or class from such requirement.