The conventional Decca Navigator system is of the type in which pairs of stations generate patterns of hyperbolic position-lines. One station, the master, is common to each pair so that a chain of three stations suffices to provide the two intersecting position-lines required for fixing. Among the advantages of this arrangement are the absence of any limit to the number of users of a single chain and the compactness of the position-fixing instrument (the receiver) which can readily be installed in the smallest craft. These two features contribute considerably to the success of Decca as an aid to surveying as well as to navigation.