BUDAPEST, HUNGARY—Researchers from Eötvös Loránd University believe that a piece of a small wooden disc discovered in an eleventh-century convent in Greenland may have been used as a “twilight compass” by the Vikings on their 1,600-mile journey across the North Atlantic from Norway to Greenland. Discovered in 1948 and known as the Uunartoq disc, some scholars originally thought it was a decorative object. But when used with a pair of crystals, or sunstones, to pinpoint the position of the sun below the horizon, and a wooden slab to help determine cardinal direction, the disc would have worked within four degrees of error. “Not the best, maybe, but it would have been a really big help,” Balázs Bernáth told Live Science.