11. The system according to claim 10 wherein the reading scan rate is a line scan rate and the reading speed detector is configured to: processing the movement of at least one eye from the eye tracker to detect line change eye movements by detecting eye movements in a direction opposite from a reading direction of a line or column in the electronic text; determine the user's line scan rate based on the detected line change eye movements and a timer, the line scan rate being a numerical value indicative of a number of lines read per unit time; and calculate an estimate of the user's reading speed based on the line scan rate and supplementary scan rate data indicative of the average or actual quantity of electronic text per line.
11. The system according to claim 10 wherein the reading scan rate is a line scan rate and the reading speed detector is configured to: processing the movement of at least one eye from the eye tracker to detect line change eye movements by detecting eye movements in a direction opposite from a reading direction of a line or column in the electronic text; determine the user's line scan rate based on the detected line change eye movements and a timer, the line scan rate being a numerical value indicative of a number of lines read per unit time; and calculate an estimate of the user's reading speed based on the line scan rate and supplementary scan rate data indicative of the average or actual quantity of electronic text per line. 12. The system according to claim 11 wherein the reading speed detector is configured to: determine the user's line scan rate as an average line scan rate over multiple successive detected line change eye movements.