Building an Arab Kamal — The Indian Ocean Navigator's Latitude Finder

The kamal is the simplest latitude-finding instrument ever devised — a small rectangular board with a knotted string through its centre. Arab and Indian Ocean navigators used the kamal from at least the 9th century AD to cross thousands of miles of open ocean by holding the board at arm's length with the lower edge on the horizon and the upper edge touching Polaris, then biting the string taut at a specific knot. Each knot corresponded to the latitude of a particular port or landmark: when the board exactly framed the angle between horizon and pole star with a given knot between the teeth, the navigator knew he was at that port's latitude and could sail due east or west to reach it. The great Arab navigator Ahmad ibn Mājid, who wrote the Kitāb al-Fawā'id (Book of Useful Things) around 1490, described the kamal as the primary instrument for Indian Ocean navigation. Portuguese sailors encountering Arab navigators in the Indian Ocean in 1498 were astonished by the accuracy of this deceptively simple device. This blueprint builds a functional kamal from a small wooden board and knotted cord, calibrated for latitude measurement by Polaris observation.