A navigation tool, called an astrolabe, discovered in a shipwreck off the coast of Oman is believed to be the oldest known example of its type.

The artefact, recovered from a Portuguese ship Esmeralda which sank during a storm in the Indian Ocean in 1503, has been identified as an astrolabe, an instrument once used by mariners to measure the altitude of the Sun during their voyages. The bronze disc measures 17.5 centimetre in diameter and is less than 2 millimetre thick.  The ship was part of a fleet led by Portuguese explorer Vasco da Gama, discovered and researched on the course of last years. Laser analysis of the artefact revealed etches around the edge of the disc, each separated by five degrees, allowing sailors to measure the height of the sun above the horizon at noon to determine their location so they could find their way on the high seas. The researchers believe it is the 108th such artefact to have been confirmed catalogued so far worldwide and is also the earliest known example by several decades.

(after BBC News, Divers 24 & Philip Koch)