Figure 6-6.—Adjusting the line of sight.4. Repeat this process until the condition isconnected.NOTE: To compensate for the above maladjust-ment, use only that part of the vertical hair that is closestto the horizontal cross hair.ADJUSTING THE LINE OF SIGHT.— In aperfectly adjusted telescope, the line of sight should beperpendicular to the horizontal axis at its intersectionwith the vertical axis. To make the line of sightperpendicular to the horizontal axis (fig. 6-6), youshould proceed as follows:1. Sight on a point, A, at a distance of not less than200 feet with the telescope normal; clamp both plates.2. Plunge the telescope and set another point, B, onthe ground at a distance from the instrument equal to thefirst distance and at about the same elevation as point A.3. Unclamp the upper motion, rotate the instrumentabout its vertical axis, sight on the first point (telescopeinverted), and clamp the upper motion.4. Plunge the telescope and observe the secondpoint. If the instrument is in adjustment, the point overwhich it is set will be on a straight line, AE, and point Bwill fall at position E. If the instrument is not inadjustment, the intersection of the cross hairs (point C)will fall to one side of the second point, B.Figure 6-7.—Adjusting the horizontal axis.5. Measure the distance BC and place a point, D,one fourth of this distance back toward the originalpoint, B.6. Move the cross-hair reticle horizontally byloosening the screws on one side of the telescope tubeand tightening the opposite screw until the vertical crosshair appears to have moved from C to the correctedposition, D.7. Repeat this operation from number 1 above,until no error is observed.8. Repeat the test described for adjusting thevertical cross hair, since the vertical cross hair may haverotated during this adjustment.NOTE: You can compensate for the abovemaladjustment by double centering (discussed in theEA3 TRAMAN).ADJUSTING THE HORIZONTAL AXIS.—When you plunge the telescope, the line of sight shouldgenerate a truly vertical plane. For this to occur, thehorizontal axis of the telescope must be perpendicularto the vertical axis. To make the horizontal axis of thetelescope perpendicular to the vertical axis (fig. 6-7),you should perform the following steps:6-7
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