About Curve Degree
You can specify the curve degree when you create or edit a curve.
The minimum curve degree is:
• At least 5 when surface curvature tangency is set for two ends.
• At least 4 when surface curvature tangency is set for one end.
• 3 when no surface curvature tangency is set.
• Low degree (1, 2) curves are possible under strict limitations:
◦ Low degree curves can only be created or edited only when 
Control Points is selected.
Control Points is selected.◦ A curve of degree 1 can only have two control points. The result is a straight line.
◦ A curve of degree 2 can have a maximum of three control points.
◦ A curve of degree 1 or 2 cannot be a closed curve.
The maximum curve degree is 15.
If you apply surface curvature tangency to a curve with less than the minimum required degree for that level of tangency, the degree will automatically change to the minimum required degree. For example, if you set surface curvature tangency to one end of a curve with a degree of 3, the curve automatically changes to a degree of 4.
When the curve degree increases, the number of control points increases by one for each degree increase. When the curve degree decreases, the number of control points decreases by one for each degree.
For periodic curves, the value for the curve degree must be an odd number. When a curve of an even-numbered degree is changed to periodic, the degree increases by one.