7.3.1 Sectional figures 

Where a figure is a cross-section of another figure, the latter should indicate the position of the section and may indicate the viewing direction by arrows at each end. In addition, in order to allow each sectional figure to be quickly identified, especially where several cross-sections are made of the same figure, each end of the cross-section line should be marked on the diagram with the same single Arabic or Roman numeral which identifies the figure in which the section is illustrated.