King John II of Portugal continued this effort, forming a committee on navigation. This group computed tables of the sun's declination and improved the mariner's astrolabe, believing it a good replacement for the cross-staff. These resources improved the ability of a navigator at sea to judge his latitude. Castilian Jew Abraham Zacut, the author of an exceptional treatise on astronomy/astrology in Hebrew, with the title "Ha-jibbur Ha-gadol", fled to Portugal in 1492. He published in the printing press of Leiria in 1496, the book "Biur Luhoth", or in Latin "Almanach Perpetuum", which was soon translated into Latin and Spanish. In this book were the astronomical tables (ephemerides) for the years 1497 to 1500, which may have been instrumental, together with the new astrolabe, made of metal and not wood as before (created and perfected at the beginning of the Portuguese discoveries), to Vasco da Gama and Pedro Álvares Cabral in their voyages to India (also passing through South America) around the open Atlantic ocean (including the Southwest Atlantic) and in the Indian Ocean. Nevertheless, the Portuguese had to hire local pilots in the Indian Ocean for several decades to guide their ships.