As a divinatory line, nine at the fifth place of Increase reads within the hexagram's overall concern with advantage in every movement undertaken, even advantage in crossing the great stream. The line occupies a place proper to its own nature in the classical doctrine that odd places favour a firm, yang line and even places favour a yielding, yin line. It is also one of the two central lines of the hexagram, the place classical reading treats as the most balanced regardless of the line's own character. Its own text, that sincere heart seeking to benefit those below, no need even to ask about it, great good fortune, and they respond with sincere hearts to acknowledge his goodness, is the particular fortune assigned to this one stage of the situation, not to the hexagram as a whole.
The fifth line corresponds by classical convention with the second line, and the two correspond here, since one line is yin and the other yang. Read together with the trigram it belongs to, Xun in the upper position of the figure, the line marks the ruling stage of the hexagram, the place classical reading treats as its centre of authority, one stage in the six stage movement the hexagram traces from its first line to its last.
A change at this line, from yang to its opposite, is the mechanism the tradition uses to move from one hexagram to another. Flipping the fifth line of Increase turns Xun into Gen while the other trigram, Zhen, stays as it is, which yields Increase's changing partner, Nourishment (King Wen 27), the hexagram this line is recorded as transforming into.