On the "Decca Navigation Chart" in the Northern European Waters

First we drew the contours of the constant probability density of the ship-position every each existent Decca Chain in the Northern European Waters, using the following formulae: P (P, R)=sinφ_P+sinφ_R-sin(φ_P+φ_R) P (P, G)=3/4 {sinφ_P+sinφ_G-sin(φ_P+φ_G)} P (R, G)=3/5 {sinφ_R+sinφ_G-sin(φ_R+φ_G)} [See Fig.2〜Fig.9 in this paper] Secondly, by means of the combination of the above mentioned contours, we made the practical "Decca Navigation Chart" by which we could select the appropriate chain and pair to find out the most accurate Decca Fix at any position in the ditto Waters. [See Fig.10 in this paper]