Contours of constant probability density have been calculated for Loran systems in different service areas, and from these some ‘Loran navigational charts’, which indicate to the navigator the best two pairs of stations to select, are drawn up. The constant probability density contours are shown in Figs 1–6 (a) and the Loran navigational charts are given in Figs 1–6 (b). The areas covered are: Fig. 1. Japan and the adjacent seas; Fig. 2. NW. Pacific; Fig. 3. Hawaii; Fig. 4. N. Pacific; Fig. 5. NW. Atlantic; Fig. 6. N. Atlantic.