VR images are usually viewed through a stereo display which is attached to the viewer’s head. This headset contains tracking technology which allows the field of view to be updated as the viewer moves. Head-mounted displays, or HMDs, display stereo images using either mobile phones or, in headsets like the Oculus or Vive, a screen for each eye. The quality of HMDs vary depending on factors like screen resolution, latency, frame rate, field of view, and the accuracy of the head tracking technology. HMDs that use mobile phones currently only track rotation (3DoF), while non-mobile headsets track the full 6DoF, allowing a more immersive experience.