I hope it was a better explain.
The check up point is not a the end of te tip [ red ] when is in contact whith the screen of table, but it check up point at the end of the pen [ black part ], as the tip did not exist.
In this way, even if you calibrate it , the pointer is alwais displaced, since varies whit the angle which you write.
Excuse me , i spanish and write in it’s difficult to me.