. Railroad construction. Theory and practice . centerand (if possible) higher than both slope-stakes, but not morethan a rod-length higher. On very steep ground this may beimpossible and each slope-stake must be set by separate positionsof the level. 78 RAILROAD CONSTRUCTION. §69. (2) Set the rod-tape at zero (, so that the 15-foot markon the back is at the index mark). (3) Hold the rod at the center-stake-(^) and note the read-ing (ni or ). Consider n to be always plus; consider d to beplus for cut and minus for fill. (4) i^mse the tape on the/ace side of the rod (71 +d). Appliedlitera
. Railroad construction. Theory and practice . centerand (if possible) higher than both slope-stakes, but not morethan a rod-length higher. On very steep ground this may beimpossible and each slope-stake must be set by separate positionsof the level. 78 RAILROAD CONSTRUCTION. §69. (2) Set the rod-tape at zero (, so that the 15-foot markon the back is at the index mark). (3) Hold the rod at the center-stake-(^) and note the read-ing (ni or ). Consider n to be always plus; consider d to beplus for cut and minus for fill. (4) i^mse the tape on the/ace side of the rod (71 +d). Appliedliterally (and algebraically), when the level is helow the roadbed(only possible for fill), (n + d) = (n2 + {—df)) =712 —df. This beingnumerically negative, the tape is lowered {df—n^. With levelat (1), for fill, {n-\d)= (n^ -\-(—df))= (n^ —dj); this being positive,the tape is raised. With level at (1), for cut, the tape is raised(ni + dc). In every case the effect is the same as if the telescopewere set at the elevation of the Fig. 45a. (5) With the special distance-tape, so held that its zero is ^hfrom the center, carry the rod out until the rod reading equalsthe reading indicated by the tape. Since in cut the tape israised (n-\-d), the zero of the rod-tape is always higher than thelevel (unless the rod is held at or below the elevation of the road-bed—which is only possible on side-hill work), and the readingat either slope-stake is necessarily negative. The reading forglope-stakes in fill is always positive. (6) Record the rod-tape reading as the numerator of a frac-tion and the actual distance out (read directly from the otherside of the distance-tape) as the denominator of the fraction. Proof. Fill. Level at (i). Tape is raised {n^—df). Whenrod is held at C/, the rod reading is +0:, which =rfi — (ni—df).But the reading on the back side of the distance-tape is also x. Fill. Level ^t (2). Tape is raised (^2 —J/), , it is lowered(df—n.^. When r
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