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 116
, AND CARE OF INSTRUMENTS. 85 when the telescope is on the meridian, then for any otherpointing of the telescope the reading of this same verniergives the true azimuth of the line. It is necessary, therefore,to have two independent movements of telescope and horizon-tal limb on the same vertical… … it is attached directly to the axis itself, for this must alwaysbe made vertical. The limb is graduated from zero to 360°, and sometimeswith a second set of figures to 90° or 180°. There are twoverniers reading on the horizontal limb 180° apart. Both theinstruments shown in Figs. 17 and 18 have…
Surveying
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