External polygon and biplot sectors
External polygon is formed with the cultivars located farthest from the biplot origin (0, 0). These cultivars are part of the corners of the polygon (cultivar markers) and are connected with straight lines. Cultivar markers are the ones with the highest response and they could be the best or the worst in some or all of the environments. Perpendicular segmented lines to each side of the polygon are drawn to divide the biplot in different sectors of cultivars and environments. The cultivar located in the corner of one sector is the winner cultivar with the highest yield in the environment or environments of this sector.