Regulation 10—Drawings.(1) A drawing which forms part of an application for a patent shall be on sheets the usable surface area of which shall not exceed 26.2 cm by 17 cm.  The sheets shall not contain frames round the usable or used surface.  The minimum margins shall be as follows—top       ...  ...  ...  ...  ...  ...  ...  ...  ...  ...  ...    2.5 cm;left side ...  ...  ...  ...  ...  ...  ...  ...  ...  ...  ...    2.5 cm;right side    ...  ...  ...  ...  ...  ...  ...  ...  ...  ...    1.5 cm; andbottom       ...  ...  ...  ...  ...  ...  ...  ...  ...  ...    1.0 cm.(2)  Drawings shall be executed as follows—(a)  without colouring in durable black ink, sufficiently dense and dark, uniformly thick and well-defined lines and strokes should be used to permit satisfactory reproduction;(b)   cross-sections shall be indicated by hatching which does not impede the clear reading of the reference signs and loading lines;(c)  the scale of the drawings and the distinctness of their graphical execution shall be such that a photographic reproduction with a linear reduction in size to two-thirds would enable all details to be distinguished without difficulty; and if the scale is given on a drawing, it shall be represented graphically;(d)  all numbers, letters and reference signs appearing in the drawings shall be simple and clear, brackets, circles and inverted commas shall not be used in association with numbers and letters;(e)  elements of the same figure shall be in proportion to each other, unless a difference in proportion is indispensable for the clarity of the figure;(f)  the height of the numbers and letters shall not be less than 0.32 cm and for the lettering of drawings, the latin and, where customary, the greek alphabets shall be used;(g)  the same sheet of drawings may contain several figures, where figures drawn on two or more sheets are intended to form one whole figure, the figures on the several sheets shall be so arranged that the whole figure that the whole figure can be assembled without concealing any part of the partial figures;(h) the different figures shall be arranged without wasting space, clearly separated from one another and they shall be numbered consecutively in arabic numerals, independent of the numbering of the sheets;(i)   reference signs not mentioned in the description or claims shall not appear in the drawings, and vice versa, the same features, when denoted by reference signs shall, throughout the application, be denoted by the same signs;(j)  the drawings shall not contain textual matter, except, where required for the understanding of the drawings, a single word or words such as "water", "stream", "open", "closed", "section on AA" and in the case of electric circuits and block schematic or flow sheet diagrams, a few short catchwords;(k)  the sheets of the drawings shall be numbered in accordance with regulation 12 (9).(3)  Flow sheets and diagrams shall be considered to be drawings for the purposes of these Regulations.