Curve Edit > Create > Duplicate Curve

Duplicates any curves that are picked when you click the tool, and any curves you click while the tool is active.

Duplicate Curve Options

Duplicate Type: No Rebuild – Do not rebuild the curve after duplicating it.

Curvature, Reduce Spans, Del Multi Knots, Uniform Knots, Match Knots – Rebuild the curve after duplicating it.

See the discussion of the Rebuild Type option of the Rebuild curve tool for information on the rebuild types and their options.

Control Options

Smoothing: After duplicating, automatically switch to the Smooth tool to allow you to smooth the resulting curve.
Interactive: Allows you to specify an arbitrary surface isoparametric curve to duplicate, rather than a visible one.
MixMax Display: Automatically create a Min-Max deviation comb between the original and duplicated/rebuilt curves.
Auto Recalc.: Automatically update the new curve when the values in the Duplicate Curve window change.

Buttons

Recalc: When Auto Recalc. is turned off, use this button to update the duplicated curve with the current values.
Undo: Undo all the changes made by the Duplicate Curve tool and return to the original curve.
Next: Finish duplicating the current curve and prompt for a new curve to duplicate.