@TheCADnoob The link is a nice write up but the command parameters should specify fit points not not control vertices since the explicit function for sine is used.
That is, spline m f 0,0 not spline m cv 0,0
Also, when choosing the delta x value for something like a trig function it would be better if the minimum and maximum values were explicitly specified.
As a side note, the attached Excel file includes a custom function I wrote for creating of B-splines from control vertices. It will duplicate the splines created in AutoCAD if the weights of vertices are all 1.0 (a B-spline and not a NURBS). The worksheet compares the accuracy of a degree 3 B-spline (AutoCAD spline) for 180°with a true sine curve. Macros must be enabled for the Excel file to use the custom Excel BSPLINE function.

lee.minardi