What is eye tracker calibration
In order for eye tracking to work as accurately as possible, the eye tracker must know more about your eyes. This is why you need to do a calibration. During the calibration the eye tracker measures how your eyes reflect light. The calibration is done by following a point, video or other graphic element that moves across the screen. This calibration data is then combined with our unique 3D model of a human eye, and together they give you an optimal eye tracking experience.
There are, however, simpler games and applications where accuracy is not as critical, that you can use without performing the calibration. Examples of these would be simple cause and effect games or other apps with big targets that are easy to click. Check this out in Eye Gaze Pathway.
If you want to know more about how eye tracking works go here.