(a) without colouring, in durable, black, sufficiently dense and dark, uniformly thick and well-defined lines and strokes to permit satisfactory reproduction; (b) indicating cross-sections by hatching and which hatching shall not impede the clear reading of the reference signs and leading lines; (c) in a scale and graphical representation, such that a photographic reproduction with a linear reduction in size to two-thirds would enable all details to be distinguished without difficulty; (d) with simple and clear numbers, letters and reference signs (brackets, circles and inverted commas shall not be used in association with numbers and letters); (e) such that the elements of the same figure are in proportion to each other, unless a difference in proportion is necessary for the clarity of the figure; and (f) such that the height of the numbers and letters are not less than 0.32 centimetre, and for the lettering of drawings, the Latin and, where customary, the Greek alphabet shall be used. (4) Where the scale is given as an exception on a drawing, the scale shall be represented graphically. (5) (a) The same sheet of drawings may contain several figures. (b) Where figures drawn on 2 or more sheets are intended to form one whole 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.