A parametric spline is a smooth curve through a series of points in space. The points through which a spline was originally drawn are called nodes. When a parametric spline was created each node was assigned a "tangent vector" by a blending function built into SURFCAM. Each vector had a direction defined by X, Y and Z coordinates and a magnitude. The combination of direction and magnitude of the tangent vectors for all the nodes defines the parametric spline.