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Figure 11-48.-Philadelphia rod.
Turning-Point Pins and Plates

Engineering Aid 3 - Beginning Structural engineering guide book
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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 steel base.  Some  are  equipped  with  thermometers,  so temperature correction can be applied. Precise rods generally contain built-in rod levels. When a rod reading is made, it is accurate only if the rod is perfectly plumbed. If it is out of plumb, the reading will be greater that the actual vertical distance between the HI and the base of the rod. Therefore, to ensure a truly plumbed leveling rod, use a rod level. Two types of rod levels that are generally used with standard leveling rods are shown in figure 11-49. The one at the left is called the bull’s-eye level, and one on the right is the vial level. Figure 11-50 shows the proper way  of  using  the  bull’s-eye  level;  the  vial  level  is attached in the same manner. Proper  care  should  be  taken  of  leveling  rods.  The care  consists  of  keeping  them  clean,  free  of  sand  and dirt, unwarped, and readable. They must be carried over the shoulder or under the arm from point to point. Dragging them through the brush or along the ground will wear away or chip the paint. When not in use, the leveling rods should be stored in their cases to prevent warping.  The  cases  are  generally  designed  to  support the reds either flat or on their sides. The rods are not to be leaned against a wall or to remain on damp ground for  any  extended  period,  since  this  can  produce  a curvature in the rods and result in unpredictable random and  systematic  errors  in  leveling. Stadia  Boards In  determining  linear  distance  by  stadia,  you observe a stadia rod or stadia board through a telescope containing stadia hairs, and note the size of the interval intercepted by the hairs. Atypical stadia board is shown Figure 11-50.-Proper attachment of a bull’s-eye rod level to the rod. Figure 11-51.-Nadia board. 11-44







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