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A Viking named Stjerner Oddi compiled a chart showing the direction of sunrise and sunset, which enabled navigators to sail longships from place to place with ease. Almgren, an earlier Viking, told of another method: "All the measurements of angles were made with what was called a 'half wheel' (a kind of half sun-diameter which corresponds to about sixteen minutes of arc). This was something that was known to every skipper at that time, or to the long-voyage pilot or kendtmand ('man who knows the way') who sometimes went along on voyages ... When the sun was in the sky, it was not, therefore, difficult to find the four points of the compass, and determining latitude did not cause any problems either." (Almgren)[citation needed]