A Secondary Node is owned by, and positioned relative to, an existing Section. It enables the user to position and connect another Section (an Attached Section) at any point along the length of the first Section (the Owning Section), rather than having to define the position of the Attached Section in ‘free space’.

They are positioned by specifying their distance from their owning Section’s Start Position, measured along the Neutral Axis towards the End Position. This distance, which is held in the Node’s ZDIST attribute, may be specified as an absolute length, as a proportion of the overall distance between POSS and POSE (i.e. a proportion of the derived length of the Section), or by reference to any marker (pin, p-point, p-line etc.), element or plane.