FIELD EQUIPMENT

stadia arc. The striding level contains a long bubble, and when attached, permits accurate leveling of the line of sight. The bubble is mounted on a metal tube with V-fittings on each end. The fittings are placed astride the telescope and bear on built-in polished brass rings on each side of the center post. A spring clip on the level grips a center pin on top of the telescope and keeps the level from falling or being knocked off during operation. A button on the side of the level releases the clip for removing the level. For checking and adjusting, the level is reversible. The striding level normally is used to establish a horizontal line of sight and to use the alidade as a level. The stadia arc assembly consists of a vertical arc mounted on the end of the left trunnion and a vernier attached to the left bearing by an arm. A level vial is attached to the upper end of the arm; a tangent screw controls the movement of the vial. Once adjusted, this vial establishes a reference from which vertical angles can be measured even if the plane table is not exactly level. The stadia arc is a vertical scale attached to the alidade. With the stadia arc, it is possible to determine horizontal distances and differences in elevation by the stadia method. 6. A new model telescopic alidade is the self-leveling, optical-reading instrument. Instead of the exterior arc and level bubble, a prism system with a suspended element and enclosed arcs is used. As long as the alidade base is leveled to within one-half degree of horizontal, the suspending element (or pendulum) will swing into position. Then the vertical arc index that is attached to it will assume a leveled position. The scales are read directly through an optical train. This combination permits faster operation. In addition, there is no chance of forgetting to index the arc bubble and introducing errors into the readings. Some of the auxiliary equipment used with a plane table consists of a coated plastic or a paper plane table sheet on which the map or sketch is drawn, drawing materials (scribing tools for coated plastic or pencils for the paper), scales for plotting distances, triangles, waterproof table covers, umbrella, and notebook. The plane table sheet is attached to the board by flatheaded, threaded studs that fit into recesses in the table and do not obstruct the alidade’s movement. instrument accessories used in connection with field measurements. FIELD TOOLS If you are running a survey across rough terrain, the essential equipment you will need are various types of tools used for clearing the line; that is, for cutting down brush and other natural growth as necessary. Surveying procedures usually permit the bypassing of large trees. Occasionally, however, it may be necessary to fell one of these. If heavy equipment is working in the vicinity, an EO may fell the tree with a bulldozer. The next best method is by means of a power-driven chain saw. In the absence of a chain saw, a one-man or two-man crosscut saw may be available. The machete and brush hook (fig. 11-32) are used for clearing small saplings, bushes, vines, and similar growth. Axes and hatchets (fig. 11-32) are used for felling trees and also for marking trees FIELD EQUIPMENT The term field equipment, as used in this training manual, includes all devices, tools, and Figure 11-32.-(A) Machete; (B) Brush hook; (C) Single-bit belt ax; (D) Single-bit ax; (E) Half hatchet. 11-35