surveying iii (topographic and geodetic surveys) - Modern Prepper

enchmark and at least one other existing benchmark and must show there is no change in their relativeelevations.(2) All first-order lines are divided into 1- to 2-kilometer sections. Each section must be runforward and backward. The two runnings of a section must not differ by more than ±3 millimeters √K,where K is the length of the section in kilometers. On all sections that are 0.25 kilometers or less inlength and which require two or more setups in each direction, a discrepancy of not more than 2.0millimeters between the backward and forward measurement is considered a satisfactory check. In thecase of a single-setup section, the checks between forward and backward runnings seldom exceed 1.0millimeters, averaging 0.6 millimeters or less.(3) When additional runs are made due to excessive divergence, the indiscriminate mean of allmeasured differences in elevation for that section is computed, excluding obvious blunders. If anymeasurement of the difference in elevation for that section is more than ±6.0 millimeters √K from theindiscriminate mean, that observation is rejected. No rejection should be made on because of a residualsmaller than ±6.0 millimeters √K, unless there is some good reason for suspecting an error in thatparticular measurement. In such cases, the reason for the rejection must be stated in the record. Afterthe rejection has been completed, the mean of all remaining forward measurements is computed andcompared with the mean of all remaining backward measurements to determine if the required accuracyhas been obtained. The mean of the means is then the final value.(4) The method and equipment used in first-order levels are designed to yield a maximum of ±1millimeter for the probable accidental error and ±0.2 millimeter for the probable systematic error in adistance of 1 kilometer.b. Second-Order Leveling. The uses of second-order leveling are also quite important, so thecriteria are only slightly less strict than those for first-order leveling. Second-order leveling is used tosubdivide nets of first-order leveling and to provide basic control for the extension of levels of the sameor lower accuracy. This order leveling is used to provide data for mapping projects, local surveys, andspecial projects, which include the positioning of radar equipment and stellar camera pads. Secondorderleveling is also used for initial missile site surveys. Second-order levels are divided into twoclasses, Class I and Class II.(1) Class I is used in remote areas where the line must be longer than 40 kilometers due to theunavailability of routes, for the development of additional or higher order networks, and for spur lines.All lines must start on previously established benchmarks of first or second order. New levels must berun between the starting benchmark and at least one other existing benchmark to prove that they havenot changed their relative elevations. Failure to check within the limit of ±8.4 millimeters √K (where Kis the distance between benchmarks in kilometers) may indicate that at least one or both of thebenchmarks must be tied in to prove the starting elevation. All Class I lines are divided into 1- to 2-kilometer sections which are run both forward and backward. The discrepancy between these runs mustnot exceed ±8.4 millimeters √K, where K is the length of the section in kilometers. When4-3 EN0593