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ADJUSTING THE TELESCOPE LEVEL. To
be able to use a transit for direct leveling and to measure vertical angles
without index error, you must ensure that the axis of the telescope level is
parallel to the line of sight. To adjust the telescope level of the transit, use
the same two-peg method that we discussed previously for the engineers level.
The only difference is that you must level the telescope carefully before each
reading. After computing the reading that should be made on the far rod (fig.
6-3), you set the horizontal cross hair on the computed reading using the
vertical slow motion screw. Then you move one end of the spirit level vertically
by means of the adjusting nuts until the bubble is centered in
the tube (fig. 6-8). NOTE: As with the engineers level, you should compensate for the above maladjustment by careful balancing of all backlights and foresights.ADJUSTING THE VERTICAL CIRCLE VERNIER. For vertical angles to be measured without index error caused by displacement of the vertical circle vernier, the vernier should read zero when the plate bubbles and telescope bubbles are properly leveled. To make the vertical circle vernier read zero when the instrument is leveled (fig. 6-9), you should perform the following steps:1. With the plate bubbles leveled, bring the telescope bubble to the center of the tube and read the vernier of the vertical circle.2. If the vernier does not read zero, loosen the capstan screws holding the vernier and move the index until it reads zero on the vertical circle.3. lighten the screws and read the vernier with all the bubbles in the center of their tubes to make sure that
Figure 6-9.Adjusting the vertical circle vernier. the vernier still reads zero and has not moved during the operation.NOTE: To compensate for the above maladjustment, you should read all vertical angles direct and reversed; then use the average of the result. This concludes our discussion of instrument adjustment. As a reminder, you should always check your surveying instruments frequently for proper adjustment and then make those adjustments either immediately or as soon as practicable. Do not put it off or you may quickly forget to do it until it is too late. Also, be sure to check the manufacturers instructions before making the adjustments described above or when you need to adjust other instruments, such as the automatic level, alidade, or hand level. |
 
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