surveying iii (topographic and geodetic surveys) - Modern Prepper

Set up and level the instrument. Read all three crosshairs as projected on the face of rod number 1, with the bubblecontinuously in coincidence. Read and record each crosshair to the nearest 0.001 meter, as shown in the example in Figure4-7, columns (7) and (13). Always read the three crosshairs in their order of magnitude onthe rod, beginning with the highest value. These values are averaged for the final values. Inthis process, the half (the difference between the top and the middle and the middle and thebottom crosshairs) and the total stadia intervals are determined and recorded. Any time thatthe half-thread intervals do not agree to within 0.003 meter, reobserve all readings. If thedifference after reobservation is exactly 3 millimeters, the divergence is acceptable. A noteshould be added in the remarks column that the foresight or backsight observation wasrepeated.(1) Check the readings taken on the Invar strip on the front of the rod by reading the centercrosshair on the back of the rod to the nearest hundredth of a foot. The mean of the three threadreadings, converted to feet, must check within 0.02 foot.(2) Instrument stations are numbered consecutively for a day's work. At odd-numberedinstrument stations, take the readings at the backsights first; at even-numbered stations, take theforesight reading first. In this method, the same rod is held on a turning point for both the foresights andbacksights, so the same rod is read first at each setup. It is the one used for the backsights at the firstinstrument station of the day's work. Use leveling platforms or metal pins driven into the ground forturning points.(3) Sections are named in their forward direction. Forward or backward denotes the direction inwhich the level line is run. The backward measurement on any section of a line running in bothdirections should be made under different atmospheric conditions from those on the forwardmeasurement.(4) Shade the instrument from the direct rays of the sun at all times. Since the wind and the sunare possible sources of error, record their direction and intensity in the level book in the spaces providedat the top of the page (as shown in Figure 4-7, (2) and (4)). An explanation of the numbers used after thewords sun and wind is shown in Figure 4-8, page 4-18.EN0593 4-16