Practical instrument adjustment: Which statements reflect good practice and realities when adjusting surveying instruments?

Introduction / Context:
Survey instruments require periodic checks and adjustments to maintain accuracy. Field personnel must understand both the limitations of the devices and the correct use of adjustment screws to avoid over-correction, damage, or unstable results.

Given Data / Assumptions:

• Adjustments may be iterative rather than one-and-done.
• Instrument condition (wear, play, looseness) affects results.
• Proper torque and technique for adjustment screws are assumed.

Concept / Approach:
Systematic errors are often minimized by iterative adjustments; a single attempt rarely eliminates them entirely. If the instrument is mechanically unstable (worn clamps, loose bearings), even correct procedures cannot hold the alignment, making satisfactory adjustment impractical. Screws must be firmly seated for repeatability, but forcing them risks thread damage and introduces stresses that later relax, reintroducing errors.

Step-by-Step Solution:

Verification / Alternative check:
Repeatability checks (face left/right) confirm whether the adjustment holds under typical instrument motions; instability shows as drifting results.

Why Other Options Are Wrong:
Each of A–C is correct; only D captures the full set of best practices and realities faced in the field.

Common Pitfalls:
Over-tightening, skipping re-tests, or attempting fine adjustments on equipment that has underlying mechanical issues.

Final Answer:
All of the above