Hi Grant,I appreciate your response and explanations.Right,the gaze within the screen area, the trackability works well. Moreover, 1)I expect wider areas can be mapped into my app’s main win and presented visibly,thus,the gaze outside the usual screen area can also be seen, that’s just like a kind of scale. And also, the current calibration mode can only be at the bottom of the screen, 2)I think it wonderful to provide more flexible modes, such on the top of the screen, and so on. At last, as my investigation, the 4c is still able to capture the gaze outside the usual screen area, but only very narrow area. If more, the trackability will be lost, so, once header turn a small degree,the gaze will lose, that should be the 4c’s work scope..Thanks again.