Curve tangents can change the curve shape, and they can create connections with another curve or surface. You can constrain the tangents of control points and of interpolation points.

A Natural tangent is calculated using the natural mathematical tangent for the defining points. This is the default for newly created curves. The tangent may change direction as you modify the defining points. A Free tangent is user-defined. A Natural tangent becomes a Free tangent as soon as you manipulate it.

When you create a tangent connection, you can select Fixed length or Proportional length. When you apply a fixed length, the Length value you set is preserved during changes to the curve, and a length parameter is created that can be edited outside Style mode. Tangent connections created before Pro/ENGINEER Wildfire 5.0 are Fixed length.

When you select Proportional length, you set the tangent length to be a proportion of the natural tangent length. A stretch parameter is created that can be edited outside Style mode. This option is the default setting for new tangent curve connections, but you can fix the length during curve editing.