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 126
ore-sight, as in this case, subtract the differ-ence from the next fore-sight, if that course and the precedingone have both their letters the same (as in this case, both be-ing !N. and E.), or both their letters different; or add the dif-ference if either the first or last letters of the two… … 108 LEVELLING, TOPOGRAPHY, AND HIGHER SURVEYING. When the compass indicates much local attraction, thedifference between the directions of two meeting lines (or the angle of deflection of one from the other), can still be cor-rectly measured, by taking the difference of the bearings ofthe two…
Surveying
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