It is difficult to properly calibrate devices whose screens are both pen and touch sensitive. One must be careful to keep their hand off the touchscreen in order to calibrate, lest an errant contact be interpreted as intentional click. This makes it extremely challenging to get an accurate calibration since there is nothing to keep the hand (and by extension, the pen) steady.

Ideally, the calibration tool should ignore clicks from devices other than the one being calibrated. Alternatively, it may suffice to ignore all clicks more than some maximum distance away from the target's center.