The variable helix feature allows a user to create a helix that can vary in diameter and pitch. The curve can also be made to follow the radius of a given set of faces. Curves are defined by design intent rather than equations. Each section of the helix is defined by pitch, diameter, and length. All changes in pitch and diameter are done in a linear manner. Non linear changes in diameter can be achieved by creating a revolved surface and selecting Match Face Radius.