Taking observations on both Face Left and Face Right with a theodolite eliminates:
Choose the correct answer
Parallax error in target sighting
Line of collimation error and horizontal axis error (by averaging FL and FR)
Levelling error in the bubble
Effect of magnetic declination
Correct Answer
B. Line of collimation error and horizontal axis error (by averaging FL and FR)
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Face Left (FL) + Face Right (FR) eliminates: (1) Line of collimation error (non-perpendicularity of line of sight to horizontal axis); (2) Horizontal axis error (trunnion axis not horizontal). Mean of FL and FR readings eliminates these. Circle graduation error eliminated by multiple sets with different initial settings.
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