Translations:Sketcher BSplinePoleWeight/30/en

Rational B-splines are created by setting a radius for the circles of the control points. That a radius has a unit must hereby ignored, the weight is always the radius in mm (or in the base length unit you set in the preferences). So a radius of 1 µm means a weight of 0.001. By default, meaning on creation time, all circles have the constraint to be equal. For the radius of the circle of the first point FreeCAD automatically sets a size constraint. Since all circles have the same radius, the set value is not important. So after creation you have a non-rational ("normal") B-spline.