The temporary adjustments of a theodolite are procedures used to ensure the accuracy and precision of measurements taken with the instrument. The following are the main temporary adjustments of a theodolite:
Leveling: This adjustment ensures that the theodolite is level in both the horizontal and vertical planes. Leveling is performed by adjusting the legs of the tripod and using the level vials to ensure that the bubble is centered in both vials.
Collimation: This adjustment ensures that the line of sight of the instrument is aligned with the center of the vertical axis of the instrument. Collimation is performed by sighting a distant target and rotating the theodolite until the crosshairs are aligned with the target.
Centering: This adjustment ensures that the axis of the vertical circle is centered over the axis of rotation of the theodolite. Centering is performed by sighting a distant target and rotating the theodolite until the crosshairs remain stationary in the field of view as the instrument is rotated.
Focusing: This adjustment ensures that the crosshairs and target are in focus. Focusing is performed by adjusting the eyepiece of the instrument until the crosshairs and target are clear and sharp.
These temporary adjustments are performed before each measurement is taken and are critical to ensuring the accuracy and precision of the measurements. They are especially important in cases where the instrument will be used over an extended period of time or in challenging environmental conditions, such as high temperatures or wind.
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