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Seaborne astrolabes were quite different to those used on land, so if da Game (or other early Portuguese arrival), then it should be easy to tell. That said, astrolabes were in use in the classical world c.4th century BCE to 4th century CE and then on into the Byzantine Empire. They were principally developed in the medieval period in the Islamic middle east, with the earliest recorded example being manufactured in the 9th century CE and the earliest surviving example dating from the 10th century CE. in non-Islamic Europe (i.e. Europe pre Reconquista) the earliest examples are 11th century. So given a find in Oman, I’d suppose the greater probability would that this is more likely to have been a local product.