1. Sight on a point, A, at a distance of not less than 200 feet with the telescope normal; clamp both plates.

2. Plunge the telescope and set another point, B, on the ground at a distance from the instrument equal to the first distance and at about the same elevation as point A.

3. Unclamp the upper motion, rotate the instrument about its vertical axis, sight on the first point (telescope inverted), and clamp the upper motion.

4. Plunge the telescope and observe the second point. If the instrument is in adjustment, the point over which it is set will be on a straight line, AE, and point B will fall at position E. If the instrument is not in adjustment, the intersection of the cross hairs (point C) will fall to one side of the second point, B.

5. Measure the distance BC and place a point, D, one fourth of this distance back toward the original point, B.

6. Move the cross-hair reticle horizontally by loosening the screws on one side of the telescope tube and tightening the opposite screw until the vertical cross hair appears to have moved from C to the corrected position, D.

7. Repeat this operation from number 1 above, until no error is observed.

8. Repeat the test described for adjusting the vertical cross hair, since the vertical cross hair may have rotated during this adjustment.

NOTE: You can compensate for the above maladjustment by double centering (discussed in the EA3 TRAMAN).

ADJUSTING THE HORIZONTAL AXIS. When you plunge the telescope, the line of sight should generate a truly vertical plane. For this to occur, the horizontal axis of the telescope must be perpendicular to the vertical axis. To make the horizontal axis of the telescope perpendicular to the vertical axis (fig. 6-7), you should perform the following steps:

Figure 6-8.Adjusting the telescope level.

1. Sight the vertical cross hair on some high point, A, at least 30 above the horizontal and at a distance of 200 feet, such as the tip of a church steeple or other well-defined object, and clamp the plates.

2. Depress the telescope and mark a second point, B, at about the same level as the telescope.

3. Plunge the telescope, unclamp the lower plate, and rotate the instrument about its vertical axis.

5. Clamp the lower plate and depress the telescope. If the vertical cross hair intersects the second or lower point, B, the horizontal axis is in adjustment. In this case, point B is coincident with point D in both direct and reverse positions of the telescope.

6. If not, mark the new point, C, on this line and note the distance, BC, between this point and the original point.

7. Mark point D exactly midway of the distance BC. CD is the amount of correction to be made.

8. Adjust the horizontal axis by turning the small capstan screw in the adjustable bearing at one end of the horizontal axis until point C appears to have moved to point D.

9. Repeat this test until the vertical cross hair passes through the high and low points in the direct and inverted position of the telescope.

NOTE: When you cannot immediately correct the above condition, you can compensate by repeating any survey procedure with the telescope reversed and then use the average of the results.