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 50
thevernier \s greater thdn a division on the limb, then by movingthe vernier forward a trifle, the next backward division on the ADJUSTMENT, USE, AND CARE OF INSTRUMENTS. 19 vernier comes into coincidence. Thus we have two kinds ofverniers, called direct and retrograde according as they are… … Fig. 5. In Fig. 5 are shown two direct verniers, such as are usedon transits with double graduations. Thus in reading to theright the reading is 138° 45^ but in reading to the left it is 221°15^ In each case we look along the vernier in the direction ofthe graduation for the coincident lines.
Surveying
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