If you’re curious to learn more about NURBS and continuity control, I’m sharing a couple of links that go more in depth on how this geometry works.
These series of articles are intended for Alias users, and although some tools and terminology is different, the theory is the same for Rhino. I would start with the “theory builder”:
http://www.aliasworkbench.com/theoryBuilders/
The section on “Golden Rules” is good too. We don’t necessarily follow all of them because some of them are specific to the needs of car body design and others are more finicky that are necessary at our skill level:
http://www.aliasworkbench.com/goldenRules/
See the rest of this site here:
http://www.aliasworkbench.com/
This article links to a somewhat comprehensive definition of NURBS
http://www.rhino3d.com/nurbs
The Wikipedia page for NURBS is also a useful reference:
https://en.wikipedia.org/wiki/Non-uniform_rational_B-spline
This has a relatively easy to follow, but very thorough discussion of the important terms:
http://www.pilot3d.com/NurbSecrets.htm
This article links to two other that are more deep in their description, with equations and formulas that are quite complex:
http://www.mactech.com/articles/develop/issue_25/schneider.html
http://web.cs.wpi.edu/~matt/courses/cs563/talks/nurbs.html
