Rotating the tangent vector around the selected location, while keeping its magnitude unchanged

To rotate the tangent vector of a curve in a certain point without modifying its magnitude, start the Curve Shape Constraint command and proceed as follows.

1	Select the curve by clicking on the location you want to edit. A handle will be displayed on the curve in the location you selected.
	You are now enabled to change the curve shape by moving the location you selected on it or by modifying the tangency conditions in the same location.
2	To rotate the tangent vector around the selected location, while keeping its magnitude unchanged, proceed as follows:

• Right-click on the tangent vector and select Set Tan Direction. The handle starts moving along as you move the mouse. Click to stop the rotation and fix the handle at its new direction.
  
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• Click on the handle middle way between the selected location (the central point of the handle) and an end point. The handle starts moving along as you move the mouse, while holding down the mouse button. Release the mouse button to stop the rotation and fix the handle at its new direction.