This feature measures the stability of the azimuth angle. The change of the azimuth angle can be compared with up and down movements of the pen, for example vertical strokes. In automated writing, the pen moves automatically based on finger movements. When we write, the azimuth angle of the pencil varies around a fixed position and is related to the size of the writing.
Research shows that children with handwriting difficulties either show bigger variation around this fixed position or they hardly show any movements. Children who tend to write large letters show big changes in the angle, and children with a cramped hand position hardly change the angle at all.