along the edge of the film. Each dot is approximately 0.015 inches in diam- eter, and is located within the frame area of the film rather than between the sprocket holes. The tuning fork maintains its frequency to about one part in 100,000, and the jitter in the individual marks is of the order of one microsecond. Means will be provided for the Observers to verify the fre- quency of these marks in terms of the velocity of sound in air. ll. Survey Data and Methods The United States has carried out a first-order survey of the entire atoll over a period of seven years. Benchmarks established around the atoll, and on stations erected above coral-heads within the lagoon, allow precise determination of the location of any new stations within a very short time. A horizontal coordinate grid is used to describe the locations of all stations within the area. The origin of the coordinate system is at a coral-head known as "Oscar''; the geographic location of Oscar is at N 11° 32! 20,254" E 162° 17! 10.944" and the local grid coordinates. in feet, are N 100,000.00 ‘E 100,000.00 In this coordinate system, the photo station on Parry is at N 54,195.00 E 133,085.00 The shot barge is expected to be within the rectangle N 138,500 # 1,500 E 74,400 + 2,500 , and the exact coordinates will be surveyed after it is in place. The horizontal distance from camera to bombis then found simply by subtracting to get the north and east differences, and taking the square root of the sum of the squares, Clearly it is not practical to check the first-order survey in a matter of a few days, nor is it necessary to check to such precision. The follow- ing procedure will be used to permit the U. N. Observers to check the survey results. c eo pre oa ab -17-