The theory and practice of surveying. Designed for the use of surveyors and engineers generally, but especially for the use of students in engineering (1886)
Johnson, J. B. (John Butler), 1850-1902 · New York, J. Wiley & sons · leaf 469
bi-section it should be as narrow as possible for distinctness. This 440 SURVEYING. is accomplished by making the width subtend an angle of fromtwo to four seconds of arc. Since the arc of one second isthree tenths of an inch for one-mile radius, an angle of fourseconds would give a target one… … Fig. 124.
Surveying
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