Why does it say One-Eyed above the calibration results?

In the calibration dialogue of Tobii Gaze Interaction Software or Tobii Eye Control Suite, it will display you the calibration results for each eye with two colored boxes. Above the boxes it states if the result is for the left eye or the right eye. If the eyetracker only detects one eye during calibration, it will instead show the same calibration result in both boxes and the text will change to One Eyed.