It is unlikely that the exploration of the open seas of the southern Atlantic was made in a single voyage, particularly when the route taken by Vasco da Gama in 1497 was significantly different from the one taken by Pedro Álvares Cabral in 1500, each being adapted to the season of departure. This adaptation shows an understanding of the cycle of yearly variations in winds and currents in the southern Atlantic. Furthermore, there were systematic expeditions pushing into the western Northern Atlantic (Teive, 1454; Vogado, 1462; Teles, 1474; Ulmo, 1486) The documents relating to the supplying of ships, and the ordering of sun declination tables for the southern Atlantic for as early as 1493-1496, all suggest a well planned and systematic activity. The most significant consequence of this systematised knowledge was the negotiation of the Treaty of Tordesillas in 1494, moving the line of demarcation 270 leagues to the west (from 100 to 370 leagues west of the Azores) with the consequence of affirming the Portuguese claim to Brazil and its dominance of the Atlantic.