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Solve for X: Deciphering Calibration Marks Made for Classified Spy Missions - 99% Invisible
Viewed from the sky or seen up close on the ground, giant X shapes and triple bar patterns scattered across the United States look equally perplexing. The former (above) are like huge treasure-map markers, but built at the scale of the map and not the ground represented. The latter (below) are even stranger, like geometrical land art,