16. The system according to claim 10 wherein the reading scan rate is a saccade rate and the reading speed detector is configured to: process the movement of at least one eye from the eye tracker to detect gaze fixation points between saccades, the gaze fixation points representing when the user's gaze has temporarily fixated without requiring detection of an exact position of the user's gaze within the electronic text; determine the user's saccade rate based on a time interval between detected gaze fixations, the saccade rate being a numerical value indicative of a number of saccades a user makes per unit of time; and calculate an estimate of the user's reading speed based on the saccade rate and supplementary scan rate data indicative of the average or actual quantity of electronic text between successive gaze fixation points.
16. The system according to claim 10 wherein the reading scan rate is a saccade rate and the reading speed detector is configured to: process the movement of at least one eye from the eye tracker to detect gaze fixation points between saccades, the gaze fixation points representing when the user's gaze has temporarily fixated without requiring detection of an exact position of the user's gaze within the electronic text; determine the user's saccade rate based on a time interval between detected gaze fixations, the saccade rate being a numerical value indicative of a number of saccades a user makes per unit of time; and calculate an estimate of the user's reading speed based on the saccade rate and supplementary scan rate data indicative of the average or actual quantity of electronic text between successive gaze fixation points. 17. The system according to claim 16 wherein the supplementary scan rate data comprises data indicative of an average quantity of text traversed per saccade for the user.