 The "tondo e quadro" device is very similar to the Arab sine quadrant ("Rubul mujayyab"), with the corner rays replicating the role of the adjustable plumb line.While the "toleta de marteloio" (and its visual counterpart, the "tondo e quadro") are designed for the explicit task of recovering an intended course, they can be used in more ways, for many classes of navigational problems, e.g.plotting out a course with multiple-bearing changes, etc.