Nobody ever took one of these to sea. That was the first thing Europeans got wrong about them. Two missionaries writing in the 1860s assumed the Marshallese were carrying charts in their canoes, and it took a German naval officer another forty years to establish that the charts never left the land. A navigator studied the model until he held the whole thing in his head, and then he sailed with nothing in his hands at all.

What the model holds is the behaviour of water, not the position of land. A swell meets an atoll, bends around it and closes again on the far side, and goes on interacting for miles beyond the last of the reef. Where two swells cross they make a node, and the line running through the nodes is called a root. One of the navigators who explained this in the 1890s said it this way. As the root leads you to the palm, this leads you to the island. The shells are where the land sits inside that pattern. The curved sticks are the water bending.

None of it was learned from the model first. A student lay blindfolded in the bottom of a canoe while it was towed in circles around a coral islet, until he could tell one swell from another through the hull with his eyes shut. The chart came afterwards, on land, to give a shape to what the body already knew. The knowledge went to a few people in each community and a chief granted the title of navigator only after a voyage had proved it. Two schools of navigators alive today build different models and still disagree about how the road between atolls works.

This is the largest of the three kinds, the one that takes in both chains rather than a single run. The Marshallese call them Ratak and Rālik, sunrise and sunset, the eastern and the western, and this chart names places across the two. They are typed onto small labels beside the shells, and whoever typed them knew what they were doing. Everything reads ATOLL except Mejit and Jemo, which read ISLAND, because those two are single islands with no lagoon. The spellings are the old anglicised ones. In Marshallese, Lae is calm water, Mājej is the eastern opening, Pikaar is to fly lagoonward, Utrōk is the southern flower. Pikinni, which the rest of the world spells Bikini, means the surface of coconuts. A navigator's own model carried no writing on it anywhere. These labels were put on by a hand other than the maker's, for a reader who was never meant to need them, and whether that happened when the chart was made or long afterwards we cannot tell you. We would rather say that than invent it.

It came out of an American estate. From 1947 to 1986 the Marshall Islands were administered from Washington, and almost everything Marshallese that left in those forty years went to the United States, carried home by Navy and contract staff at Kwajalein, by Trust Territory teachers, and from late 1966 by Peace Corps volunteers sent to teach English. Two of the names typed onto this chart are Pikinni and Utrōk. Between 1946 and 1958 the United States detonated sixty seven nuclear devices in these islands, twenty three of them at Bikini, and when the largest went off on 1 March 1954 the fallout crossed Rongelap and Utirik. The chart does not know any of that. It was made to teach somebody how to find land by the way water moves, and the atolls on it were places before they were anything else.