The previous paper described how the two components of a compound system could be combined, through the medium of a pictorial display, in a common coordinate system. This essential process can be carried out by an airborne digital computer with considerable advantage, and with a degree of refinement—e.g. data smoothing— which would be beyond the scope of the simpler manually-operated system. In other words, the computer can introduce a second mode of compound operation which differs from the simple relationship between position-fixing and D.R. systems described earlier, in that by continuously combining the incoming information from the position-fixing system and the dead-reckoning device it can deliver an output of a substantially higher quality than that of either input taken separately.