This is very similar to the 3D-QuickSpline macro. The difference is that this one calculates a path for a closed bspline curve based on the control points. It is intended that a closed 3D polyline will be used for the control point frame. This means the first and last vertices of the polyline are coincident. This is simply to make the use of the macro more logical. In actual practice, the last vertex is not included in the calculation, since it would just be a dulplicate of the first. So in fact the last vertex could be place anywhere.