The spline of the sketch 3Dsketch3 is defined with 2 points.
So, it's very strange that it's in black, since a spline needs at least 3 points
But I want a tangent relation with the circle of the Surface-Revolve2, and then I get some red.
It's very funny, because when a curve is totally defined, it remains in blue (see my thread
and I can drag this curve all around the sketch.
When the curve has still degress of freedom, it is in black, and it's impossible to get what I want otherelse than to create a construction line (impossible to define others relations than with lines, with some tangent vector of a spline) !!!!