Picking up points with digitizer pen

Hi,
When I was picking up points using a Microscribe digitizer pen, I noticed that when the pen rotates, even though the tip is fixed at a point, the coordinates are changing. This way, my coordinates will depend on how I hold my pen. Is it right? How should I correct this?

Any thoughts?

How much is the variation?

It would not stay exactly the same but should fall within the accuracy stated for the arm.