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Figure  11-14.-Theodolite  reticle.
One-Second   Theodolite

Engineering Aid 3 - Beginning Structural engineering guide book
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vertical circle images into a single field of view. In   the   DEGREE-GRADUATED   SCALES   (fig. 11-16),  the  images  of  both  circles  are  shown  as they would appear through the microscope of the 1-min  theodolite.  Both  circles  are  graduated  from 0°  to  360°  with  an  index  graduation  for  each degree  on  the  main  scales.  This  scale’s  graduation appears  to  be  superimposed  over  an  auxiliary  that is graduated in minutes to cover a span of 60 min (1°).  The  position  of  the  degree  mark  on  the auxiliary scale is used as an index to get a direct reading in degrees and minutes. If necessary, these scales can be interpolated to the nearest 0.2 min of  arc. The   vertical   circle   reads   0°   when   the theodolite’s  telescope  is  pointed  at  the  zenith,  and 180° when it is pointed straight down. A level line reads  90°  in  the  direct  position  and  2700 in  the reverse. The values read from the vertical circle are referred to as ZENITH DISTANCES and not vertical  angles.  Figure  11-17  shows  how  these zenith  distances  can  be  converted  into  vertical angles. Figure 11-17.-Converting zenith distances into vertical angles  (degrees). In   the   MIL-GRADUATED   SCALES   (fig. 11-18),  the  images  of  both  circles  are  shown  as they  would  appear  through  the  reading  micro- scope  of  the  0.2-mil  theodolite.  Both  circles  are graduated from 0 to 6,400 mils. The main scales are marked and numbered every 10 mils, with the Figure  11-16.-Degree-graduated  scales. Figure 11-18.-Mil-graduated scales. 11-23







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