It was a simple nautical instrument used to orientate the navigation. It consisted of a disc with radius which indicated the direction of the twelve winds (Aparctias, Boreas, Kaikias, Apeliotes, Euros, Euronotos, Notos, Libonotos, Lips, Zephyros, Argestes, Thrascias). It is most likely that the centre had a rotating vane (strip, statuette, Triton, etc.) and at its circumference it had twelve oblique pegs as on the later anemoscope of Eftropiou.

SOURCES: Ptolemy, The Great Syntaxis of Astronomy (Almagest), Archimedes, Psammitis.