Eye tracking white sclera (limbus tracking). It presents another challenge for vertical eye movements due to obstruction of eyelids. Eye-tracking setups vary greatly: some are head-mounted, some require the head to be stable (for example, with a chin rest), and some function remotely and automatically track the head during motion. Most use a sampling rate of at least 30 Hz. Although 50/60 Hz is more common, today many video-based eye trackers run at 240, 350 or even 1000/1250 Hz, speeds needed in order to capture fixational eye movements or correctly measure saccade dynamics. Eye movements are typically divided into fixations and saccades
Guild Wars: Eye of the North 40 new armor sets, and 10 new "heroes", in addition to the new items, weapons, and titles added as usual in every "Guild Wars" campaign. It is in part intended to act as a bridge from "Guild Wars" to "Guild Wars 2" and introduces the new races of the "Norn" (dwellers on the icy slopes of the Shiverpeak Mountains to the north) and "Asura" (inhabitants of the southern part of the Maguuma Jungle), both of which would later become playable in the sequel. "Eye of the North" continues the "Prophecies" story, which is told in three acts. In Act I,