Scale
Don’t mix the Scale channel up with the Length channel. Scale scales the hair, including its form, and does not cut it off.
The part in the example above was rendered, from left to right, with Scale set to 40%, 70% and 100%, respectively.Use Variation to define the maximum random variance in the scale of the hair. A value of 0% will scale all hairs equally.
Use this slider to define to what degree randomly selected hair will be affected by the other Scale settings.
In the example above, a grayscale gradient was used to scale the hair.