After the shot barge is in place the Observers will measure angles, by means of a Wild T-2 phototheodolite on the barge, between a number of identifiable islands. Furthermore an aerial photograph will be taken, including the barge and a grid of buoys, and also some of the easily iden- tifiable islands in the vicinity. | From the measured angles, and with the help of the aerial photograph, the Observers will spot the barge on two charts of the atoll, and will simply scale the distance to the'Parry photo tower from the charts. Two published charts are available: the first was published by the Japanese Government in 1943, and the second by the United States Navy in 1944 (Hydrographic Office, Chart No. 6033), Although these charts differ by about one-half mile as to the absolute geographic latitude and longitude of the Eniwetok Atoll, and although some of the islands have changed shape markedly from erosion and deposition, distances between given points scaled from the two charts generally agree to better than 0.5 percent. Scaled measurements from the USN Hydrographic Chart, and from a photostatic copy of the Japanese map, show very good agreement between the two. Three pieces of info.mation are available to establish the scales of each chart: a) scale of distances (nautical miles in the U.S. chart and kilometers in the Japanese), b) distance between parallels of latitude 10minutes apart; and c) distance between parallels of longitude 10-minutes apart. We know from the standard navigational literature 7,8 that 10 min- utes of latitude, centered at latitude 11°-30', is 60,483 feet, and of longi- tude 59,657 feet. Scaling from the charts gives scale factors in feet per inch for the three methods: Method U.S. Japanese 8,340 8,370 10-Minute Latitude 8,330 8, 530 10-Minute Longitude 8, 340 8, 460 8,337 8,453 Scale (nautical miles or kilometers) Average.... U.S. Department of Commerce, Coast and Geodetic Survey, Special Publications Nos. 8 and 241. U.S. Government Printing Office (1949). Bn. Bowditch, American Practical Navigator. Office (1943). -18- U.S. Hydrographic