The Eternal Pose represents one of the navigational tools existing in the One Piece world that guide ships to specified islands within treacherous waterways like the Grand Line. Unlike the Log Pose, which normally changes its magnetic field to point toward the next island on a set route, the Eternal Pose fixes itself permanently to indicate the direction of a single predetermined destination.
An Eternal Pose resembles something along the lines of a glass orb mounted on a wooden base. It contains a compass needle inside the orb and a name of the island to which it is supposed to point on the base. Such a design allows for easy identification and usage, even in the chaotic magnetic environment of the Grand Line.
The Eternal Poses are of the utmost importance in the world of One Piece. They represent a reliable way to sail across a sea where conventional compasses cannot even function because of the unstable magnetic fields of the Grand Line. On page 128 of the manga, an Eternal Pose to Alabasta is requested by none other than Marine Officer Smoker himself. This goes to show just how essential a tool it is for any pirate or governmental force.
Probably one of the most memorable points regarding an Eternal Pose appearing in the series is when the Straw Hat Pirates gets one that would point towards Arabasta, from the mysterious Miss All Sunday, later revealed as Nico Robin. Luffy promptly destroyed the Eternal Pose in a dramatic moment that showed just how much determination and unpredictability was bundled into his person; he preferred to travel on his own rather than take a back route.
These Eternal Poses have become quite popular collector items among fans of One Piece. Bandai has released a total of series of replica Eternal Poses, where the second series includes designs for places like Dressrosa, Zou, and Whole Cake Island. These replicas are designed to be "unaffected by all the elements of the Grand Line or New World," much like their in-universe counterparts.
Given this, Eternal Poses, in particular, would be in great demand by traders and the Marines throughout the One Piece world. With them, one could get to important places directly by avoiding the island-to-island route prescribed by a Log Pose. Such navigation skill greatly gives one an edge over others on these huge and often dangerous seas of the Grand Line.
The Eternal Pose concept has also fueled many works from fans and role-play situations. For example, a person developed a role-playing game known as "One Piece: Eternal Pose," which is set several decades after the events of the story canonized, thereby letting gamers forge new adventures in the One Piece world.
It should be noted, however, that Eternal Poses, as invaluable tools as they are, have their limitations: they point to a single, specified island and cannot be reprogrammed. Thus, for travelers going to multiple places, or in those complicated travels which require more than one destination, they must have not one but many Eternal Poses or pair Eternal Poses with Log Poses to reach their destinations.