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 195
half-degrees,and the angle is laid off byholding the centre at the vertexof the angle, with the plainedge, or the o and 180 degreeIG* 44 line on the given line from which the angle is to be laid off. In the full circle protractor, shown in Fig. 45, there is amovable arm with a vernier reading to… … 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
Surveying
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