. Railroad construction : theory and practice : a textbook for the use of students in colleges and technical schools . 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. (2) Set the rod-tape at zero (, so that the 15-foot markon the hack is at the index mark). (3) Hold the rod at the center-stake (J5) and note the read-ing (rii or 712). Consider n to be always plus; consider d to beplus for cut and minus for fill. 78 RAILROAD CONSTRUCTION. §70. (4) i2at
. Railroad construction : theory and practice : a textbook for the use of students in colleges and technical schools . 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. (2) Set the rod-tape at zero (, so that the 15-foot markon the hack is at the index mark). (3) Hold the rod at the center-stake (J5) and note the read-ing (rii or 712). Consider n to be always plus; consider d to beplus for cut and minus for fill. 78 RAILROAD CONSTRUCTION. §70. (4) i2at^6 the tape on the/ace side of the rod (n + cO- AppHedliterally (and algebraically), when the level is below the roadbed(only possible for fill), (?i + c?) = (712 + ( —d/)) =712 —d/. This beingnumerically negative, the tape is lowered (df—n^). With levelat (1), for fill, (n + d) = (^1 + (— c?/)) = (rii — d/); this being positive,the tape is raised. With level at (1), for cut, the tape is raised(ni + c?c). 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 forslope-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 +x, which =rf^ — {n^—df).But the reading on the back side of the distance-tape is also x. Fill. Level
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