A treatise on surveying, comprising the theory and the practice ; (1887)
Gillespie, W. M. (William Mitchell), 1816-1868, Staley, Cady, 1840- [from old catalog] ed · New York, D. Appleton and company · leaf 373
e upside down,end for end, and half-way around horizontally, and sight again.Half the sum of the two readings is the correct one, no matter howmuch the instrument is out of adjustment (assuming the collars to be of equal size) ; forthe errors then canceleach other. This is theone used principally…
Surveying
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