Captain García-Frías has made the following comments on the discussion of his recent paper (this Journal, 18, 141) contributed by E. S. Calvert and S. H. Hollingdale.

Captain García-Frías observes that while Calvert and Hollingdale recognize that this paper combines his earlier suggestion for a sector rule with a set of manœuvring rules, they have failed to recognize the fundamental distinction between the structural and operational aspects of an encounter; his proposed manœuvring rules deal with the operational aspect. These rules differ from the manœuvres they have themselves proposed in that they depend only on the bearing of the target as seen on the radar at a distance of 2 miles; they derive from his sector rule and do not require a quantitative estimate of the miss distance. His rules are only the same as their manœuvres for the case of a steady bearing since their manœuvres also require the sign of the miss distance.