Fig. 3.

Illustration of the variability that may be contributed by asynchrony with monitor refreshes. Eyetracker samples, taken at the time indicated by the downward arrow, will have different delays until they are reflected on the screen, depending on whether they are taken early or late in the refresh cycle. This example assumes a 60-Hz refresh rate and a 4-ms rendering time (blue bar). The shortest latency will be when the eyetracker is sampled in time for the image to finish rendering just before the refresh deadline (a), which is 4 ms in this example, whereas the longest latency will be when this deadline is just missed (b), leading to a latency of approximately 20 ms. In other cases (c), the latency will be somewhere in between