# For True Difference in Elevation Between Two Points

By BYJU'S Exam Prep

Updated on: September 25th, 2023

For true difference in elevation between two points A and B, the level must be set up

1. At any point between A and B
2. At the exact mid-point of A and B
3. Near the point A
4. Near the point B.

Answer: B. At the exact mid-point of A and B

## For true difference in elevation between two points A and B, the level must be set up at the exact mid-point of A and B.

Solution

For true difference in elevation between two points A and B, the level must be set up at the exact mid-point of A and B as this will eliminate the error due to earth’s curvature and error due to refraction. By setting the level at the midpoint, we evenly divide the error resulting from the earth’s curvature and refraction while measuring the reduced levels of both A and B.

RL of A = BM + S1 (Staff reading) + error

RL of B = BM + S2 + error

Difference between A and B = S2 – S­1

So, we can observe that the error is getting cancelled out.

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