This report concludes a series of previous reports on minimal-time ship routing, dealing both with the problem of determining the least-time track (Bijlsma en Van Rietschote, 1972, I, II, III) and with that of the computation of wavecharts from windcharts (Bijlsma en Folkers, 1973). It contains an (experimental) method for the solution of the remaining problem: to bring into agreement, by taking into account observations of ships, windcharts of the Atlantic Ocean derived from pressurecharts, with those used by the Routing Office (see chapter 1). With the solution of this problem we are in a position to compare optimal routes, obtained both in a manual way (by Routing Office) and in a computational way (way the automated system) starting from the same pressurecharts (chapter 2).