The name is perfect. "Etak" refers to a system of navigation used by Micronesian and Polynesian seafarers to navigate from island to island in the vast Pacific Ocean. Much like this device, it operates by "augmented dead reckoning" (as it says in TFA).
The etak system of navigation involves navigating by stars and ocean swells to get the heading, but a key issue when navigating by dead reckoning over long distances is that if you're a fraction of a degree off you may miss your destination and never know it, so it's also vitally important to know how far you've gone. This is hard when there are no landmarks. The navigators estimated their distance by using intermediary islands off to the side, which they viewed as coming towards them (from their point of view, the navigator stays motionless on the open ocean while the world moves towards them) and past them. These reference islands were called etaks.
However, confusingly, the etaks were generally not visible, being beyond the horizon, and sometimes did not even exist. The navigators would have named etaks that they pictured being just over the horizon, whether they were there or not, and would track their procession past their boat. When the set number of etaks had passed, they would know they were in the vicinity of the destination island. If they were not at the right time of day for birds to be out, they would then hang out in the area waiting to spot the birds leaving or returning at dawn or dusk.
So the system involves dead reckoning plus a system of turning the navigators' own well-developed intuition of how far they had travelled into a formalized system of generally-invisible islands that they used as a mental model to externalize this intuition.
(My knowledge of this is from Cognition in the wild, Hutchins, E., 1995.)
Edit: D'oh, I should have finished TFA. This is described at the end, although more roughly.