Tobii Pro X3-120, Product Description

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Appendix A
Glossary
Monocular/
binocular Monocular data shown is based on data from the participant’s dominant eye only. Binocular data is
the average of the two eyes.
Gaze precision Describes the spatial angular variation between a set of consecutive gaze samples. Gaze precision
can be measured under various conditions.
Gaze accuracy
Describes the angular average distance from the actual gaze point to the one measured by the eye
tracker. Gaze accuracy can be measured under various conditions.
Sampling rate Number of eye tracking data samples per second.
Total system
latency The duration from mid-point of the eye image exposure, to when a sample is available via the API on
the client computer. This includes half of the image exposure time plus image read-out and transfer
time, processing time and time to transfer the data sample to a client computer.
Time to tracking
recovery for blinks When a participant blinks, the eye tracker loses the ability to track eye gaze because the eye is
covered by the eyelid. If the pupil is occluded for only a short period, the system will regain tracking
immediately when the pupil becomes visible again, but only if the participant has maintained
approximately the same head position during the blink. Data during blinks are only lost when the
pupil is occluded, i.e. during the eyelid movement itself or when the eye is closed.
Time to tracking
recovery after lost
tracking An eye tracker working in a natural user environment may occasionally lose track of the participant’s
eyes, e.g., when the participant completely turns away from the tracker. If a period of a few hundred
milliseconds elapses during which the eye tracker is unable to detect the eyes in close proximity to
where they were last detected, the eye tracker will start searching for the eyes within the entire
head movement box. The stated measurement is the typical time to tracking recovery in such a
situation. If the eye tracker is unable to detect the eyes of the participant even after about one
minute, the system will enter a “slow search” mode, leading to larger recovery times.
Freedom of head
movement
Describes an area ( width x height in cm) where at least one eye is within the eye tracker’s field of
view.
Operating distance
Describes the range of distances (minimum and maximum) between the participant’s eyes and the
surface covering the eye tracker sensors at which eye tracking can be done while maintaining
tracking.
Eye tracking
processing unit Gaze data calculations are performed by firmware embedded in the eye tracker or in a separate
processing unit.
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Appendix A Glossary Tobii Pro X3–120 Eye Tracker Product Description v.1.0.2 - en-US