A separate rectangular grid system was adopted locally on each of the three experiment islands, and computations of coordinates of working points for scientific structures are based thereon, Coordinates of working points for scientific structures are based thereon. Coordinates were arbitrarily assigned to the Sandstone zero points as follows: Runit, N 15000, E 1000; Aomon, N 10000, E 5000; Engebi, N 2000, E 4000, Therefore the grid coordinate system for any one experiment island is independent of that for any other experiment island, although each rectangular local grid extends to and includes all adjacent islands, points, photo towers, etc., referred to a given experiment, The adoption of a separate local grid system for each experiment island was necessary in order to avoid delays while primary triangulation of the Atoll was being completed, Eventual computations were based on the final overall triangulation survey of the entire Atoll, to which the zero line on each experiment island was tied by position and angle, thus placing all related stations in each experiment in their true geometrical positions on each local rectangular grid, free from distortion due to any meridianal convergences, The final locations of all scientific structures for the 27 different users involved the preparation of 58 separate drawings and 204 revisions after the drawings were completed and signed. Some of these separate changes and revisions covered scores of stations, as shown in detail on the table of revisions listed on each drawing, These changes and revisions were made pursuant to relocations ordered in many verbal and written directives from J-Division, and to conform to shifting locations indicated in the several re-issues of the Instrumentation Charts received from time to time, Each time a structure was shifted, a new computation of coordinates vas required, so that on the whole the number of precise computations was increased over the basic requirement by many thousands. In scme cases, changes requested by one User interferred with locations of structures selected by other Users, thus setting in motion a chain of revisions requiring approval of two or more Users before final positions could be firmed up. Other revisions necessarilyoccurred where new structures were located on remote islands before field survays were received showing their topographic poeition relative to their parent ex-~ periment island, Because of the great number of revisions requested by Users for the relocation of scientific stations (often while construction was in pro- gress in the field) it was in many cases impossible to supply construction forces with revised location plans immediately. To avoid delay and waste, coordinates for the working points for the stations were calculated and entered on the Architectural and Structural Department drawings sent to the field in advance of revised location plans, This enabled construction forces to continue their building work without waiting for the next revised set of Civil Department drawings, 5 156