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 196
ADJUSTMENT, USE, AND CARE OF INSTRUMENTS. 167 The three-arm protractor, Fig. 46, has one fixed and twomovable arms by which two angles may be set off simulta-neously. It is used in plotting observations by sextant of two … Fig. 45. angles to three known points for the location of the point ofobservation. This is known as the three-point problem andis discussed in Chap. X.
Surveying
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