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GATE 2026 CE (CE1) – Question 43

Geomatics Engineering · Distance and angle measurement, levelling, traversing, triangulation, total station · 2 marks · Multiple choice

Locations $P$ and $Q$ are separated by a wide valley. The difference in levels of locations $P$ and $Q$ measured by a levelling instrument stationed near $P$ is 3.0 m. The same instrument stationed near $Q$ measures the difference in levels $P$ and $Q$ as $-1.0$ m. Assume that the atmospheric refraction is same during the measurements. The true difference in levels (in m) of locations $P$ and $Q$ is

  1. 1.0
  2. 1.5
  3. 2.0
  4. 4.0

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Show answer and explanation

Correct answer: (C) 2.0

Explanation

In reciprocal levelling the true difference is the mean of the two observed differences, which cancels the error from curvature and refraction. The two readings measure the difference in opposite directions, so we take the sign into account: $\frac{3.0 - (-1.0)}{2} = 2.0$ m.