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Engineers  Level  Adjustments - 14071_115
Transit Adjustments - 14071_117

Engineering Aid 2 - Intermediate Structural engineering guide book
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Figure  6-1.—Adjusting  the  level  tube. ADJUSTING THE LEVEL TUBE.—  The  vertical axis of rotation of the instrument is the basis for all adjustments   to   the   engineer’s   level.   When   the instrument is set up and leveled the vertical axis of rotation and the longitudinal axis of the level tube should be  perpendicular  to  one  another.  If  they  are  not perpendicular, then the vertical axis cannot be made truly vertical. Adjustment of the level tube makes the axis of the level tube perpendicular to the vertical axis. To check and adjust the level tube, you should follow the  procedures  below: 1.  Setup  the  instrument  and  approximately  level the  bubble  over  each  pair  of  opposite  leveling  screws. Then carefully center the bubble over one pair of screws, as shown in view A, figure 6-1. 2.  Rotate  the  instrument  180°.  If  the  bubble remains  centered,  then  the  level  tube  is  in  proper adjustment.  If  the  bubble  does  NOT  remain  centered note the movement of the bubble away from center (view B, fig. 6-1). 3. Bring the bubble half the distance back to the center of the tube by turning the capstan nuts at one end of the tube (view C, fig. 6-1). 4. Relevel with the leveling screws (view D, fig. 6-1) and rotate the instrument again. Repeat Step 3 above if the bubble does not remain at the center of the tube. 5. Check the final adjustment by noting that the bubble remains in the center of the tube during the entire revolution  about  the  vertical  axis. NOTE: When the level tube is out of adjustment, you can compensate for it by releveling the instrument before each sighting. ADJUSTING   THE   HORIZONTAL   CROSS HAIR.— For the horizontal cross hair to lie in a truly horizontal plane when the instrument is leveled, the horizontal  cross  hair  must  be  perpendicular  to  the vertical axis. To make the horizontal cross hair (fig. 6-2) lie in a plane perpendicular to the vertical axis, you should perform the following steps: 1. With the instrument carefully leveled, sight one end of the horizontal cross hair on a well-defined point at least 250 feet away. Turn the telescope slowly about the vertical axis, using the slow motion screw. If the cross hairs are in adjustment, the horizontal cross hair will stay on the point through its entire length. 2.  If  it  does  not  stay  on  the  point,  loosen  two adjacent reticle capstan screws and rotate the reticle by lightly tapping two opposite screws. 3. Sight on the point again. If the horizontal cross hair does not stay on the point through its entire length, rotate the ring again. 4.  Repeat  this  process  until  the  condition  is satisfied. NOTE: To compensate for the above maladjust- ment,  you  should  use  only  that  part  of  the  horizontal cross hair that is closest to the vertical hair for all sightings. ADJUSTING THE LINE OF SIGHT.—  For a perfectly adjusted level, the line of sight is parallel to the axis  of  the  level  tube.  When  the  level  meets  this condition,  the  line  of  sight  will  generate  a  truly horizontal  plane  when  the  instrument  is  rotated.  When Figure 6-2.—Adjusting the horizontal cross hair. 6-4







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