System works by strobing 3 IR illuminators every frame. On even frames, it uses the centre illuminator (located around the camera lens) and on odd frames it uses the 2 side illuminators. On even frames, the pupil appears bright, since the IR light is actually bouncing off the back of your eye, like red eye effect. On odd frames, your pupil appears dark. The difference between the two allows us to isolate and track the pupil in real time. Additionally, the glints (reflections of the IR illuminators) of the dark frame are tracked, and these, plus the info on the pupil, is calibrated to screen position using a least squares fitting process for an equation that provides a mapping of glint/pupil position to screen position.