For a third of a century many and varied studies on sea water have been concentrated upon a single accessible shallow-water station in the English Channel, EI, supplemented by more extensive excursions usually designed to test working hypotheses. This concentration of effort has been richly rewarded. In deep-water oceanography a similar approach is appropriate; a standard station, ‘Cavall’ has therefore been selected in the north-eastern Bay of Biscay in 4700 m of water at lat. 46° 30' N., long. 8° 00' W., nominal, a position worked by the Danish Research Vessel ‘Dana’ in 1922 and 1930. It is not only the nearest deep water position to Plymouth but it has best possible coverage by the Decca Navigator system. For our experimental programme it is essential that the station positions be maintained and repeated precisely. To achieve this a working Decca chartlet (Fig. 1) on a scale of 1:20,000 has been prepared for each station from a portion of the Admiralty Decca Lattice chart no. L 1104. On this a circle of radius one mile is inscribed. Throughout operations the ship is maintained within this circle by stopping work when necessary and steaming back on Decca co-ordinates towards the centre, or beyond to pre-compensate expected drift.