Can I just ask a really basic, possibly irrelevant and pedantic question, please?

Why is the horizontal line in this sketch fully defined? The glossary defines fully defined as "cannot be moved. Fully defined sketch entities are shown in black."

But grab any of the 3 vertices and drag them and the 'fully defined' line will move. Ok the end point of the line is blue, so you can easily figure out that only the length of the line can change. (You can make it flip direction.) But at the end of the day that line has 1DoF just like the dimensioned line.

Is anything in the underlying SW behaviour here useful to understand?

This is a good example of degrees of freedom in geometry. In the most reduced form, this line segment is really three pieces of geometry in a 2D space. There is an infinite line and two end points which must remain coincident to the line.

The line (y=mx+b):

- A horizontal relation defines the orientation of the line (m=0).

- Coincident to the origin (b=0).

The line is fully defined. For any X value Y is always zero. It should appear in black on the screen.

The Points (x,y) coincident to the line:

- One point is coincident to the origin (x=0,y=0). The point is black and should report its state as fully defined.

- The other point is coincident to the line (y=0). The x value of the point is variable. It should report that it is under defined and remain blue. The user may drag the point anywhere as long as Y=0.

Best Regards,Ditmars VEINBACHS

R&D SolidWorks, Modeling, Development Senior Manager