When Dwell is the interaction method and you want to select a button twice (i.e.- spelling with a double letter like "cool"), it's easiest to blink after you've selected the button the first time.
The MyTobii P10 is designed to only select a button once per dwell, to limit the number of accidental repeats. Another technique is to briefly look away from the button and then return your gaze to that button.
