Many dates can be found for the appearance of the first Mariner's astrolabes. The earliest date, 1295, is offered by the Majorcan astronomer Ramon Llull. Later dates center around the late 15th century, with Samuel Purchas claiming that it was adapted for marine navigation by Martin Behaim, a mariner not considered a trustworthy source by some historians. In any event, the instrument was certainly known by the end of the 15th century. Nevertheless, the creation and perfecting of the mariner's astrolabe is attributed to Portuguese navigators during the beginning of Portuguese discoveries. The earliest known description of how to make and use a sea astrolabe comes from Martín Cortés de Albacar’s "Arte de Navegar" published in 1551, although the basic principle is the same as that of the archipendulum used in constructing the Egyptian pyramids.