Planmeca ProMax 3D Max with ProTouch Technical Manual page 135

Technical manual
5.e. When the C-arm is at 180° location according to the user
interface, place a second mark on the tape in the crossing point of
the laser crosshairs on the ball phantom.
5.f. The rotating centre is between the two points you have drawn.
5.g. Manually line up the lasers by moving the lenses, until the
crossing point of the lasers remains motionless throughout a 180
degree movement of the C-arm.
NOTE
When the C-arm can turn without the lasers' crossing point shifting
in orientation, the crossing is at the C-arm rotating centre.
6. Continue by touching the 2. Mark a reference point option.
Mark the laser's crossing point.
7. Continue by touching the 3. Calibrate the front light option.
Manually adjust the front laser to the two marks.
5 Panoramic and 3D calibrations
Planmeca ProMax 3D Max 129