Figure 6-3.—Two-peg test method.the line of sight is not parallel to the axis of the leveltube, then you must adjust the line of sight. The methodused for adjustment is known as the two-peg test (fig.6-3). This method requires you to do the following steps:1. Setup and level the instrument (first setup, fig.6-3). Drive stake (peg) A about 150 feet away, then drivestake B at the same distance in the opposite direction.2. Take a rod reading a on stake A and a rod readingb on stake B. With the instrument exactly halfwaybetween the two stakes, b-a is the true difference inelevation between the stakes.3. Move the instrument close to stake A (secondsetup, fig. 6-3) so that the eyepiece is within a half inchfrom the rod. Then, by sighting through theobjective-lens end of the telescope, take a rod reading con stake A. Next, take a rod reading d on stake B in thenormal manner. If the instrument is in adjustment, d-cwill equal b-a.4. If the instrument is out of adjustment, calculatewhat the correct rod reading e should be on the fartherrod B (e = c + b - a). Set the rod reading e with a targetfor accurate reading. Move the horizontal cross hair tothe correct reading (on target) by loosening the correctvertical screw and tightening the opposite screw.5. Check the horizontal cross hair adjustmentagain. The ring may have rotated during this adjustment.6. Rerun the peg test to check the adjustment.NOTE: The compensation for the above maladjust-ment is careful balancing of your backlights andforesights.Transit AdjustmentsYou must be capable of performing six commonlyperformed tests and adjustments of the transit. All testsand adjustments of the transit are made with theinstrument mounted on its tripod and setup in the shade.You must make these tests periodically and in thesequence in which they are discussed in the followingparagraphs. When one of the tests indicates that anadjustment is necessary, you must make this adjustmentand then you must repeat all previous tests beforeproceeding with the next test.6-5
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