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 levelling, readings are taken from both ends of a line to eliminate errors like curvature of the Earth and collimation errors. However, the error due to atmospheric refraction is not entirely eliminated. This is because refraction varies with atmospheric conditions and is not symmetrical between the two reciprocal sightings.
Thus, the residual error that remains is primarily due to refraction.