surveying iii (topographic and geodetic surveys) - Modern Prepper

(8) When a leveling line is complete to a point which is to hold the elevation of the lineovernight or longer, establish at least two points with at least one instrument setup apart. When theleveling is continued from or to such a pair of points, set up the instrument midway between them, andtake rod readings on each point to determine if either of them has been disturbed. If the new differencedoes not agree with the first determination, leveling must be extended to other points to verify thestability of the point used in carrying the elevation ahead. When establishing a pair of points, decidewhich one is to be the TBM and which one is to be the checkpoint. To avoid confusion, carry theelevation forward over the point selected as the TBM. The difference in elevation between the points ofthe pair should be at least 0.3 meter. Then, should confusion occur in carrying the elevation aheadthrough the line, any blunder would be so large that it would stand little or no chance of remainingundetected when the line is tied out or a circuit is closed.(9) Permanent benchmarks should be established at about 2-kilometer intervals throughout theline. When needed, TBMs should be placed between PBMs. Depending upon the terrain and the controlto be extended from the line, it may be necessary to break up the line into shorter sections so that it willonly be necessary to rerun a small section of the line if it busts.b. Recording Precise (Spirit) Leveling Data. All observations of either first- or second-orderleveling are recorded in the field book, as shown in Figure 4-7, page 4-17. The circled numbers in thefigure correspond to the numbers shown in the following recording procedures:(1) Enter the date.(2) Enter the direction of the sun, with respect to the direction of the running of the line. Ifconditions are cloudy, the abbreviation should be 0 (refer to Figure 4-8).(3) Enter the designation of the level-line section.(4) Enter the strength of the wind (refer to Figure 4-8).(5) Enter the time.(6) Number the instrument stations (not turning points) consecutively throughout the day.(7) Record the backsight readings to the nearest 0.001 meter.(8) Carry the mean reading to one more place than the thread reading. The mean is the averageof the three readings for each rod reading.(9) Enter the reading of the middle thread on the back of the rod to the nearest 0.01 foot.4-19 EN0593