When you blend two surfaces together, you can specify surface continuity and bulge
magnitude.

Set SURFACEASSOCIATIVITY to 1 to create a relationship between the blend surface and
the originating curves.

The following prompts are displayed.

Select surface edge

Selects an edge subobject or a surface or region (not the surface itself) as the first
and second edges.

Chain

Selects contiguous, connected, edges.

Continuity

Measures how smoothly surfaces flow into each other. The default is G0. Select a value
or use the grip to change the continuity.

Bulge magnitude

Sets the roundness of the blend surface edge where it meets the originating surface.
The default is 0.5. Valid values are between 0 and 1.