THREE EASY STEPS FOR THEODOLITE TEMPORARY ADJUSTMENT

THREE EASY STEPS FOR THEODOLITE TEMPORARY ADJUSTMENT Temporary adjustments: These are those adjustments carried out at every set-up of the instrument before observations are made. The following actions constitute the temporary adjustment: 1. Setting up the instrument over the ground mark. 2. Levelling up the instrument. 3. Clearing of parallax and focusing. 1. SETTING OVER THE GROUND MARK. a. Spread out the tripod legs and mount the theodolite b. Spread the tripod legs over the ground mark, make sure the plumb bob is approximately over the ground mark. c. Continue to adjust the tripod legs and at the same time watch the circular bubble until the instrument is fully set over the ground mark. d. If the instrument has an in- built optical plummet it should be used at this point to check the accuracy of setting over the ground mark. 2. LEVELLING THE INSTRUMENT. Levelling of the instrument is carried out as follows: a. Place the longitudinal axis of the bubble tube parallel to any two of the foot screws. Using the two foot screws bring the bubble to the centre of its run. Note: The bubble runs to the high side of the instrument. b. Turn the instrument through 900 and again bring the bubble to the centre of its run using the remaining foot screw. c. Rotate the instrument through 1800 and observe the position of the bubble . if it remains at the center of its run, it is then properly levelled. 3. CLEARING OF PARALLAX AND FOCUSING. a. To focus and clear parallax, point the telescope at a light background example the sky. b. Focus the cross hires using the eye piece until they form clear, sharp image. c. Point the telescope at the first station to be observed, focus and check for parallax by moving the eye across the eye piece. The instrument is now ready for observation of the station occupied.