After his visit to Ogygia, Odysseus built the astrolabe to find Ogygia again and rescue Calypso as an old man in Ithaca. It was one of Odysseus' last inventions, but he could never get it to work as Odysseus lacked a crystal from Ogygia which would act as a homing beacon for the device. Odysseus would lament that he never took a crystal with him and called the astrolabe his biggest what-if. It was stolen while he was sleeping by the Kerkopes.
After defeating the Kerkopes, Leo Valdez looks through their treasure and discovers an old astrolabe which is badly damaged and seems to be missing a few pieces, but fascinates Leo anyways. Passalos and Akmon explain that it was built by Odysseus as an old man in Ithaca and they stole it. However, it doesn't work due to a missing crystal. Leo isn't sure why he wants it as it's obviously broken and not what Hecate meant for them to find, but he claims the astrolabe for himself anyways.
After landing on Ogygia, Leo remembers the astrolabe and he suspects that Odysseus had built it to find the island again. However, he remembers that the astrolabe is still on the ship and that the dwarves had warned him that it didn't work because of a missing crystal.
Before leaving Ogygia, Leo has Calypso chip off some of the crystal in her cave and explains that once he figures out how to rebuild Festus, he can handle an improved guidance system. Leo begins to explain about the astrolabe and the crystal, choosing not to mention Odysseus, but Calypso is convinced that he can't return as the rules state that no man ever finds the island twice.
After reuniting with his friends and learning of Festus' permanent activation, Leo is elated and begins to say something about the crystal and the navigation system but stops himself. Later, as the Argo II sets sail for Athens, Leo tinkers with Festus' mechanical brain, muttering about the crystal and the astrolabe as he does so.
Leo keeps the astrolabe and the crystal in a drawer in Groucho, one of his tool cabinets on the Argo II. Leo laments his inability to figure out how to wire them together, having hoped that the Seven's visit to Odysseus' home in Ithaca would give him some clues. However, while Leo has to succeed where Odysseus failed, he knows that he has the crystal to act as a homing beacon which Odysseus had lacked.
After getting the Physician's Cure, Leo opens an access panel on the engine of the Argo II containing the astrolabe which now has the crystal attached. Determined to fulfil his vow to Calypso, Leo brings the navigation device online and sets a twenty-four hour timer on the astrolabe.
Following Leo's death and subsequent resurrection by Festus, he opens the access panel in the bronze dragon's neck where the astrolabe is humming away, the crystal pulsing like a neon heart. Checking the navigation readings on Festus' compass and GPS, Leo is pleased to discover that they are completely messed up. Descending below the clouds, Leo is elated to discover that Festus was able to use the astrolabe to bring them to Ogygia.