With the primary stations of the horizontal control survey as a basis, additional shore stations on the various islands were located and targets erected. Two observers and a recorder were aboard the cable barge, and as cable was laid, the course of the barge was located by taking a series of simultaneous sextant angles to three visible shore stations. The shore stations were plotted to scale on a chart, and by setting off the angles obtained in a three-arm protractor and adjusting its positions on the chart until each arm bisected a shore station, it was possible to plot the locations of the barge at the instant the observations were taken. This portion of the Project required many man-hours, but the results obtained were consistent with requirements. LOCATION OF SPECIAL STRUCTURES AND INSTRUMENTATION First order traverses were measured on the three experiment islands with 50-meter Lovar tapes, the angles with a l-second Wild theodolite. (See Figures 5.8-6, 5.8-7, and 5,88.) Each chaining buck was a substan- tial post set in concrete, and after traverse adjustment, positions were computed for the marks on each of these posts. These traverse systems served as a framework from which the working points of all scientific and test structures were staked. To guard against errors in maps, calculations, or field work which would result in probable displacement of a station from its planned position and resultant distortion of scientific results, the following method of construction staking was used. When maps arrived at the Jobsite fixing station locations, all co~ ordinates were checked to see if the azimuths and distances from zero would in fact develop them, A staking diagram was then prepared for the use of the field party, with a bearing and distance computed from the traverse stake nearest the station; and bearings were computed from the working point of the station to two or three other traverse stakes. After staking the working point, the field party was required to set up on it and measure the three or four angles around that point (with the line to zero required) to make sure that they checked the computed angles. These being in order, they proceeded to stake out the structure itself. This was followed by the instrumentation phase, which included locating certain points before the tests and rechecking after the tests were completed, Work started on Special Measurement Survey Points, Military Struc- tures for Engebi and Muzin on December 13, 1950, with a survey crew of five men - two frim Holmes & Narver and three from the Army personnel assigned to the Sandia group. The work was divided into three parts: Station 3.1.1; Stations similar to 3.3.3; and isolated groups such as the 3.2 series. The initial planning and detailed layout of the work was appreciably retarded because of lack of plans and because of insufficient information concerning the scope of the work. As finally determined, there were some 1,900 survey points established, requiring in excess of 11,000 individual measurements. 5-69