choice of some other rate of fall for tha particles, From the test of the method against the Bikini patterns, it was clear that it was good enough for the purpose at hend. It appeared that differences between forecast and actual winds would be likely to produce much larger errors than those inherent in the assumptions. 5. In application, the method is not as tedious as right appear, The standard hodograph plot, giving the location of central particles falling at 5,000 ft per hour, is prepared for the briefing as a matter of course. It can be superimposed on a ten tires magnified atoll map, allowing for the 50 ,000 ft per hour fall rate assumed in the method. With a ruler of corresponding scale, the distances S, along the eig~sag path to each of the height points on the hodograph ean be quickly measured or this can be done by summation of "hodograph*® winds if these are more readily accessible. Likewise, the distances from the altitude points on the hodograph to points of fall-out interest can be quickly measured with the ruler, giving the values of r. compute p and q. Knowing S and r, one can easily With the aid of a family of curves of 1 {a} P p* 2 vs q (see Fig. 1) for several values of p, one can rapidly interpolate the values that must be added up at any location, The exponential factor drops off very rapidly with q, and after working out a few cases, one can tell, from an inspection of the hodograph-on-atoll plot, some of the altitude points that can be neglected in the computation, 6. Fig. 2 and Table 1 dllustrates the application of the method to NECTAR shot, using the winds observed at shot time. The points on Fig, 2 marked 10, 20, 30, are the 10,000 ft, 20,000 ft, - — - altitude points on the hodograph for particles falling 50,000 ft per hour. A partiole starting, for example, at 30,000 ft above ground zero, and falling under the influence of winds but not diffusion, * would land at the point rarked 30. " COPIED/DOE + LANL pe The value of 8, the horizontal distance Gj