In this paper Claud Powell, formerly of the Decca Navigator Company, discusses the antecedents of modern radio position-fixing systems whose position lines are of hyperbolic form. The paper was presented at an Ordinary Meeting held in London on 22 April with Rear-Admiral D. W. Haslam in the Chair.

Until very recently in human history, the fixing of position for navigational and kindred purposes depended principally upon the measurement of angles. An escape from the limitations of this essentially visual process had to await the development, through advances in electrical and later in electronic engineering, of what E. W. Anderson has termed the ‘timing of waves’. This classification covers virtually all the non-visual methods of deriving a line of position, for example the measurement of range by timing the roundtrip of a signal travelling at a known speed to a reflector or transponder and back; the measurement of ‘pseudo-range’ by comparing the times of signal transmission and reception according to local clocks; and the differential measurement of range to two known points some distance apart by timing the interval between the reception of synchronized signals transmitted from those points.