18. Particulars of drawings. - Drawings shall be prepared in accordance with the following requirements, namely: -
(a) Drawings shall be executed with indelible black ink.
(b) Each line shall be firmly and evenly drawn, sharply defined and shall be of the same strength throughout.
(c) Section lines, lines for effect and shading lines, shall be as few as possible and shall not be closely drawn.
(d) Shading lines shall not contrast too much in thickness with general lines of the drawings.
(e) Sections and shading shall not be represented by solid black or washes.
(f) Drawings shall be on a scale sufficiently large to show the inventions clearly and only so much of the apparatus, machine or other matter shall appear to achieve this object. If the scale is given, it shall be drawn and not denoted by words. No dimensions shall be marked on the drawings.
(g) The figures shall be drawn preferably in an upright position with regard to the top and bottom of the sheet.]
(h) Reference letters and numerals, and index letters, symbols and numerals used in conjunction therewith, shall be bold, distinct and not less than 0.3 centimeter (one-eighth of an inch) in height. The same letters or numerals shall be used to indicate the same parts in different views where the reference letters or numerals are shown outside the figure, they shall be connected by fine lines with the parts to which they refer.
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