The spline help line can be placed like the poly help line. The lines between the vertices are not straight but curved to follow a smooth line between the vertices. In the start and end point there are draggers which can be used to change the line towards the start and end point.
Fig. 279 A closed spline help line. In the start and end point are draggers to change the line
To move the complete spline help line after it is defined once, hold down the ALT key while the mouse is above one vertex and holding down the left mouse button.
Fig. 280 Move the complete poly line by holding down the ALT key
