When simultaneous position lines are unobtainable a running fix or transferred position line is generally used. This method depends for its accuracy on the true assessing of course and speed. If, instead of transferring one of two position lines, three are obtainable, only the course need be assessed and used to obtain a position. It is assumed that the speed is constant, or nearly so—a reasonable assumption.

The need for the rapid reduction of astro-sights has been constantly stressed for use in high speed aircraft outside radio coverage. The method described here is a combination of precomputation of altitudes and graphical representation of intercept from a given position. By this method a fix can be plotted at the instant of time for which it has been precomputed.

The paper reviews some of the major problems which have been encountered in the development of airborne direction finding equipment, and describes, in rather more detail, the latest electrical and mechanical improvements which have been evolved to provide the modern, fast moving aircraft with a more rapid or instantaneous position indication.

Various methods of utilizing the information provided by the direction finder are discussed and questions of calibration and ultimate accuracy considered.

The introduction into both the Royal Navy and the Royal Air Force of the air navigational equipment that is at present envisaged emphasizes the need for a reliable and accurate compass. Further, since no compass can be expected to give completely accurate information in all conditions of use, the errors that are likely to arise and their magnitudes must be known. Before an error can be determined, it is first necessary to define what may be regarded as an error, and then to determine its magnitude as accurately as possible. Gone are the days when an expression such as ‘plus or minus two degrees’ would be regarded as satisfactory. The determination of compass accuracy to a tenth of a degree is now an accepted requirement.

The use of Consol at long ranges in ships is hampered by the lack of facilities for accurate plotting. Of necessity ocean charts (scale 1:1,000,000 to 1:12,000,000) are used; and on these it is not practicable to plot running fixes, lay off position lines from celestial observations or to compare a succession of cross bearings with any degree of accuracy.

When Consol bearings can be plotted on a large scale chart and used in conjunction with other position lines, such as Marcq. St. Hilaire, lines of soundings, m.f./d.f., &c, they are of assistance in defining an observed position; this is especially so in conditions of poor visibility, such as prevail in the approaches to the British Isles and in the North Atlantic.

The publication of the paper Astro-fix by Computation by Oliver C. Collins in the April number of the Journal serves as a reminder that the observation for the determination of the latitude from two altitudes, usually known as the double altitude problem, is one of some celebrity in the history of navigation.

The following notes on the subject may be of some interest although they are far from complete, having been compiled from such books as happened to be readily available, and can only be considered as an introduction to the subject.