Brilliant explanation from Aga -she again, sorry I admire her.
Accuracy and precision are not synonyms words. She explains both at http://www.rosenfeldmedia.com/books/eye-tracking/blog/the_most_precise_or_most_accur/:
"The accuracy of an eye tracker is the average difference between what the eye tracker recorded as the gaze position and what the gaze position actually was. We want this offset to be as small as possible but it is obviously unrealistic to expect it to be equal to zero. Accuracy is measured in degrees of visual angle. Typical accuracy values fall in a range between 0.5 and 1 degree."
"Precision (aka "spatial resolution") is a measure of how well the eye tracker is able to reliably reproduce a measurement. Ideally, if the eye is in the same exact location in two successive measurements, the eye tracker should report the two locations as identical. That would be perfect precision. In reality, precision values of currently available eye trackers range from 0.01 to 1 degree. These values are calculated as the root mean square of the distance (in degrees of visual angle) between successive samples.