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FAQ: Why can't I calibrate the edges / corners of my screen?
Dan
Support Specialist
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Joined: Aug 2020
Posts: 469

#1
09-09-2020, 08:52 AM
Difficulties with calibration, particularly with the edge or corner points is typically due to a sub-optimal arrangement of the screen, participant and camera.  If the Display monitor is too close, if the participants eyes are not aligned with the top 25% of the screen, or if the camera is placed improperly (e.g too low), or some combination of these issues, then you may find it difficult to calibrate / validate certain targets. Typically calibration issues that are due to the screen being too close / high are most apparent when trying to calibrate the top corners of the screen. This is because the participants eyes are forced to rotate beyond the trackable range of the camera. Please see the following thread for further details about the trackable range:

What is the Trackable Range and why is it important?

  • Make sure that the calibrated area of the Display monitor is within the trackable range of your EyeLink system. Our online Trackable Range Calculator is a very useful tool in this respect.
    • The EyeLink system's trackable range is 32° x 25° for all systems with the exception of the Tower Mount which has a trackable range of about 60° x 40°.
    • For the Desktop mount, a quick and simple rule to find the minimum viewing distance for the Display monitor is to multiply the width of the screen, in millimeters, by 1.75. The result should roughly be the distance that the Display monitor needs to be from the participant's eyes for the entire Display monitor to be within the trackable range. So a standard 22" Monitor which is approximately 50cm wide would need to be at least 88 cm from the participant's eyes.
  • Make sure that the camera placement relative to the participant position is correct. The images below illustrate the proper camera placements for various systems. Please note the images on the right side - when looking at the monitor from the participant's perspective there should be no visible "gap" between the bottom of the monitor and the top of the camera:
EyeLink Portable Duo
   

EyeLink 1000 Plus
   

EyeLink 1000