Rule 46
Form of the drawings

(1) On sheets containing drawings, the usable surface area shall not exceed 26.2 cm x 17 cm. The usable or used surface shall not be surrounded by frames. The minimum margins shall be as follows: 

(2) Drawings shall be executed as follows: 

(a) Drawings shall be executed without colourings in durable, black, sufficiently dense and dark, uniformly thick and well-defined lines and strokes. 

(b) Cross-sections shall be indicated by hatching which should not impede the clear reading of the reference signs and leading lines. 

(c) The scale of the drawings and their graphical execution shall be such that electronic or photographic reproduction with a linear reduction in size to two-thirds will allow all details to be distinguished without difficulty. If, exceptionally, the scale is given on a drawing, it shall be represented graphically. 

(d) All numbers, letters, and reference signs appearing on the drawings shall be simple and clear. Brackets, circles or inverted commas shall not be used in association with numbers and letters. 

(e) Generally, all lines in the drawings shall be drawn with the aid of drafting instruments. 

(f) Elements of the same figure shall be proportional to one another, unless a difference in proportion is indispensable for the clarity of the figure. 

(g) The height of the numbers and letters shall not be less than 0.32 cm. For the lettering of drawings, the Latin and, where customary, the Greek alphabets shall be used. 

(h) The same sheet of drawings may contain several figures. Where figures drawn on two or more sheets are intended to form a single figure, the figures on the several sheets shall be so arranged that the whole figure can be assembled without concealing any part of the partial figures. The different figures shall be arranged without wasting space, preferably in an upright position, clearly separated from one another. Where the figures are not arranged in an upright position, they shall be presented sideways with the top of the figures at the left side of the sheet. The different figures shall be numbered consecutively in Arabic numerals, independently of the numbering of the sheets. 

(i) Reference signs not mentioned in the description and claims shall not appear in the drawings, and vice versa. Reference signs to features shall be consistent throughout the application. 

(j) The drawings shall not contain text matter. Where indispensable to understand the drawings, a few short keywords, such as "water", "steam", "open", "closed" or "section on AB", may be included. Any such keywords shall be placed in such a way that, if required, they can be replaced by their translations without interfering with any lines of the drawings. 

(3) Flow sheets and diagrams shall be deemed to be drawings.