Difficulty: Medium
Correct Answer: All of the above
Explanation:
Introduction / Context:Theodolites measure horizontal and vertical angles with high precision. Proper geometry among the instrument axes is essential; otherwise, observed angles will contain systematic errors. The “perfect adjustment” conditions summarize the required orthogonality and plane constraints among axes and sighting lines.
Given Data / Assumptions:
Concept / Approach:For perfect adjustment: the vertical axis must be perpendicular to the trunnion axis so that vertical motion is truly in a vertical plane; the line of collimation must be perpendicular to the trunnion axis so that vertical circle motions do not change collimation; and as the telescope is raised or lowered, the line of sight should remain in a single vertical plane—ensuring correct vertical angle measurement and elimination of lateral sweeping errors.
Step-by-Step Solution:
Confirm vertical axis ⟂ trunnion axis via standard checks (spirit levels/auto levels).Adjust the line of collimation to be ⟂ trunnion axis using collimation tests (e.g., two-peg or reciprocal checks for tilt scopes).Verify vertical plane sweep by sighting a high and low point on the same vertical line; adjust if necessary.Re-check after adjustments as changes can couple between conditions.Verification / Alternative check:Reversing face observations (face left/right) and obtaining consistent angles indicate near-perfect adjustment.
Why Other Options Are Wrong:Any single condition alone is insufficient; all must hold simultaneously to avoid systematic angular errors.
Common Pitfalls:Assuming temporary leveling alone ensures perfect geometry; internal axis relationships also require adjustment.
Final Answer:All of the above
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