This option takes each toolpath contour and uses the given tilt curve to tilt each point of the toolpath contour gradually to the tilt curve.
Gradually means here the following:
At the start of a toolpath contour, the tool axis is tilting exactly to the start of the tilt curve. At the half-way (middle) of the toolpath contour, the tool axis is tilted to the midpoint on tilt curve (halfway point). Accordingly, at the end of the toolpath contour, the tool axis will be tilted to the end of the tilt curve.
Note, that a typical toolpath contains MANY toolpath contours. So the gradual tilting will happen for EACH of this toolpath contours.
Please note that the fixed tilt angle value can be changed by collision control operations in order to avoid collisions.