Question

In reciprocal levelling, the error which is not completely eliminated is due to

• A. Curvature
• B. Refraction
• C. Non-adjustment of line of collimation
• D. Parallax

Hint:

Even though reciprocal levelling minimizes errors, atmospheric refraction—being variable—is not fully cancelled out.

Answer 1

The Correct Option is B

In reciprocal leveling, the primary aim is to eliminate errors that can arise when taking measurements between two points when a large distance or obstruction is involved. By taking observations from both directions between the points, certain errors tend to cancel out. However, some errors remain that cannot be entirely eliminated. The errors considered in reciprocal leveling include:

Curvature: This refers to the earth's curvature affecting the horizontal line of sight. In reciprocal leveling, this error can be largely eliminated as it equally affects readings taken in both directions.

Refraction: Light bending in the atmosphere causes a slight deviation of the line of sight. Though reciprocal leveling reduces this, it does not completely eliminate it due to atmospheric variability being uneven in different conditions.

Non-adjustment of line of collimation: Errors due to the line of sight not being perfectly horizontal are mostly minimized since measurements in both directions average out this error.

Parallax: Resulting from improper eye positioning, this error is usually corrected through careful observer techniques and equipment adjustments.

Of these errors, refraction is the one not entirely eliminated in reciprocal leveling. The varying atmospheric conditions along the line of sight result in inconsistent refraction effects that cannot fully balance out even with reciprocal observations.