Drawings suitable for publication in a patent, known as formal drawings, can be filed any time after the filing of the patent application including any time within three months of the Notice of Allowance. The only rule is that no new matter can be injected into the drawings when they are placed into formal condition by a patent illustrator. Formal drawings do not include dimensions and are not drawn to scale.

Note: A patent application can be filed with a sketch drawn on a napkin in a restaurant, on the back of an envelope, and so on. Such drawings are known as informal drawings.