Compute Normal Like SOP Sweep

I played with SOP Spring, the normal next step is to create a SOP Sweep and Skin.

I was impress by the Normal calculation of the point in the SOP Sweep versus use SOP Attribcreate to compute the Normal.

What is the method of the SOP Sweep to get a nice Normal like that ?
How can i reproduce this ?

A little scene for comparaison.
Thx
SweepNormal.2.toe (4.73 KB)