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GATE 2017 CE (CE1) – Question 28

Geomatics Engineering · Distance and angle measurement, levelling, traversing, triangulation, total station · 1 mark · Multiple choice

An electronic distance-measuring instrument has accuracy $\pm(a\ \mathrm{mm}+b\ \mathrm{ppm})$. Which statement is correct?

  1. Both a and b remain constant irrespective of measured distance.
  2. a remains constant and b varies in proportion to measured distance.
  3. a varies in proportion to measured distance and b remains constant.
  4. Both a and b vary in proportion to measured distance.

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Show answer and explanation

Correct answer: (B) a remains constant and b varies in proportion to measured distance.

Explanation

The accuracy has a fixed component of $a$ mm and a distance-dependent component of $b$ parts per million. For a measured distance $D$ metres, the latter contributes $bD/1000$ mm. The archived key selects B, interpreting “b varies” as the absolute error contribution of the ppm term. Strictly, the coefficient $b$ itself is constant; its error contribution, not its numerical ppm specification, scales with distance. This wording ambiguity is retained explicitly.

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