Hi @ pilipapla119,
within the Tobii Tech SDK, the calibration processes are taken care of by the Tobii Interaction and the specifics of the calibration results are not publicly exposed.
For these purposes we provide the Tobii Pro range of eye trackers, targeted for research where the full range of calibration and eye tracking metrics are available. Apologies for the inconvenience.
That being said, there have been a number of comprehensive studies of eye tracking accuracy using EyeX (I could not find one for REX) which you can find @ http://link.springer.com/article/10.3758/s13428-016-0762-9
Perhaps this information will be of use.