The plane of occlusion (vertical plane) is positioned parallel to the floor. The Frankfort plane (superior border of the external auditory meatus to the infraorbital rim), Tragal-canthus plane (tab in ear to outer corner of the eye), and the Ala-tragus (corner of nose to tab in the ear) plane are used to align the vertical position of the head as well. Some machines provide a horizontal alignment light to help assess the proper vertical position of the head.
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