An important nautical manuscript in the Bibliothéque Nationale, Paris, containing a number of separate sections on Portuguese navigation methods, and written in the early sixteenth century, has been translated into modern Portuguese and edited by Professor Albuquerque of Coimbra. It is the Livro de Marinharia of André Pires, a Portuguese pilot only known by this collection, of a small part of which he was the actual author. The 13th section, which is quite short, deals with the ‘Balestilha of the Moors’, i.e. the kamal. The use of this title confirms the point, for which there is some other evidence, that although the quadrant and the (sea) astrolabe were the official navigating instruments on Portuguese ships, the cross-staff or balestilha was known and used. The principle of the kamal was, of course, that of the cross-staff. A wooden rectangular tablet was held up with one edge on the horizon, the other on the heavenly body. A knotted cord running from the centre of the tablet was held taut between the observer's teeth, and all he had to know was the meaning of the knot in his mouth in terms of ports and landmarks. The first knot—nearest the tablet—measured the ‘altura’ of Mascat, which was east-west with Diulcende, on the coast of Diul in India. The fifth knot marked the altura of the Curia Muria Is., east—west with Dabul, and so on.

The use of the Greenaway grid (curved) lines has enabled us to measure grid directions correctly on a Lambert chart (in middle latitudes). However, due to the fact that some charts are printed with only straight grid lines (such as the NAT 3071), a transport rate correction was devised which is supposed to combine both the correction for Earth rotation and the correction required because of the straight grid lines.

Whilst the idea is an interesting one, a basic mistake is introduced which leads to serious errors in grid direction measurement.

There are occasions when, because of the density of shipping and/or lack of sea room, ships navigating by radar in thick weather cannot avoid passing within a distance of two miles, the least distance usually considered desirable. In such a situation a simple plan of procedure and of avoiding action, if possible to devise, should greatly reduce strain on the navigator and so increase the safety of navigation generally. Also, if such a plan came to be generally followed, safety would be further enhanced, because each navigator would know what the others were likely to do.