Figure 11-49.-Types of rod levels.and has the scale inscribed on the strip of Lovar metal.A precise rod usually has a tapering, hardened steelbase. Some are equipped with thermometers, sotemperature correction can be applied. Precise rodsgenerally contain built-in rod levels.When a rod reading is made, it is accurate only ifthe rod is perfectly plumbed. If it is out of plumb, thereading will be greater that the actual vertical distancebetween the HI and the base of the rod. Therefore, toensure a truly plumbed leveling rod, use a rod level.Two types of rod levels that are generally used withstandard leveling rods are shown in figure 11-49. Theone at the left is called the bull’s-eye level, and one onthe right is the vial level. Figure 11-50 shows the properway of using the bull’s-eye level; the vial level isattached in the same manner.Proper care should be taken of leveling rods. Thecare consists of keeping them clean, free of sand anddirt, unwarped, and readable. They must be carriedover the shoulder or under the arm from point to point.Dragging them through the brush or along the groundwill wear away or chip the paint. When not in use, theleveling rods should be stored in their cases to preventwarping. The cases are generally designed to supportthe reds either flat or on their sides. The rods are not tobe leaned against a wall or to remain on damp groundfor any extended period, since this can produce acurvature in the rods and result in unpredictable randomand systematic errors in leveling.Stadia BoardsIn determining linear distance by stadia, youobserve a stadia rod or stadia board through a telescopecontaining stadia hairs, and note the size of the intervalintercepted by the hairs. Atypical stadia board is shownFigure 11-50.-Proper attachment of a bull’s-eye rod level tothe rod.Figure 11-51.-Nadia board.11-44
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