http://membres.lycos.fr/bobois/Tuts/Extrusion_par_bev_ob/Ext1_Ext2/Ext1_Ext2_en.html
Better than I thought, quite a few interesting things there.
The documentation on those parameters is sparse and I had to experiment a whole lot : I feel that I have it right but that wasn’t a 10 years study so, if you ever found that I erred on some point, especially about that ‘Width’ parameter, consider it your duty to inform me and anybody else by the same token.
Thanks.
Ciao.
018_effet_de_ctrl_a_toujours_fidèle.jpg this image does no exist 
about width, well, it “scales” the curve relativly to the tangent, so using resizing can only replace width if your using a circle as you did.
good tutorial yet again 
Martin
Yes, I left an accent dragging. It should work by now.
about width, well, it “scales” the curve relativly to the tangent,
Hence the effet at the center…
So it’s good to have both.
The tut will be enhanced by tonight.
good tutorial yet again
Martin
Thanks