A treatise on levelling, topography, and higher surveying (1876)
Gillespie, W. M. (William Mitchell), 1816-1868, Staley, Cady, b. 1840, ed · New York, D. Appleton and company · leaf 63
n-hill side. Try this by levelling over two screws, setting the instru-ment so that one pair of opposite plate-screws shall point inthe direction of the line, but do not be too particular; it is awaste of time. Doing this produces sights of unequal length. The rodbeing about twice as high as the… … necessary on slopes so steep that the rod is too near the levelto be read. If this be impossible, keep notes of the lengthsof the sights to the turning-points, backward and forward,and as soon as possible take sights unequal in the contrarydirection till the differences ot lengths balance the…
Surveying
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