# Pen tilt

Pen tilt refers to the angle of the writing instrument during the handwriting process, which can vary over time. In a coordinate system which is determined by the writing surface plane ${\displaystyle \{X,Y\}}$ and the vertical pen-tip movement along the ${\displaystyle \{Z\}}$ axis, all three two-dimensional planes can be discerned, and the angular signals can be delivered by a digitizer: