marks. When you cannot see the next lower foot markthrough the level instrument, you signal or ask therodman to raise for red. The rodman should slowlyraise the rod until the next lower red number comesinto view.NOTE: The feet measurements on the Philadel-phia rod are in red.Target ReadingConditions that hinder direct reading, such as poorvisibility, long sights, and partially obstructed sights,as through brush or leaves, sometimes make itFigure 15-45.—Target.necessary to use targets. The target is also used to marka rod reading when numerous points are set to the sameelevation from one instrument setup.Targets (fig. 15-45) for the Philadelphia rod areusually oval, with the long axis at right angles to therod, and the quadrants of the target painted alternatelyred and white. The target is held in place by a C-clampand a thumbscrew. A lever on the face of the target isused for fine adjustment of the target to the line ofsight of the level. The targets have rectangularopenings approximately the width of the rod and0.15 feet high through which the face of the rod maybe seen. A linear vernier scale is mounted on the edgeof the opening with the zero on the horizontal line ofthe target for reading to thousandths of a foot. Whenthe target is used, the rodman takes the rod reading.When sighting through the level instrument, thelevelman motions either up or down so that the rodmancan place the horizontal separation of the target in linewith the horizontal cross hair of the instrument. Whenthe horizontal separation and the horizontal cross haircoincide, the levelman waves ALL RIGHT.After the levelman signals the all right, the rodmantightens the target clamp. Then the rodman holds therod on the point again to ensure the target has notslipped and “waves” the rod by pushing it about a footaway from and towards his body to see if the rod wasinitially held in an absolutely vertical position. Thelevelman should recheck the target reading. If thehorizontal cross hairs do not coincide, the target mustFigure 15-46.—Zero elevation point.15-26
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