The transit (fig. 11-6) is often called theuniversal survey instrument because of its uses. Itmay be used for measuring horizontal angles anddirections, vertical angles, and differences inelevations; for prolonging straight lines; and formeasuring distances by stadia. Although transits ofvarious manufacturers differ in appearance, they arealike in their essential parts and operations.The engineer’s transit contains several hundredparts. For-descriptive purposes, these parts may begrouped into three assemblies: the leveling headassembly, the lower plate assembly, and the uppermany plate or alidade assembly (fig. 11-7).Leveling Head AssemblyThe leveling head of the transit normally is thefour-screw type, constructed so the instrument can beshifted on the foot plate for centering over a markedpoint on the ground.Lower Plate AssemblyThe lower plate assembly of the transit consistsof a hollow spindle that is perpendicular to the29.242Figure 11-6.-An engineer’s transit.11-14
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