Multiple choice

A benchmark has been established at the soffit of an ornamental arch at the known elevation of 100.0 m above the sea level. The back sight used to establish height of instrument is an inverted staff reading of 2.105 m. A forward sight reading with normally held staff of 1.105 m is taken on a recently constructed plinth. The elevation of the plinth is

  1. 103.210 m

  2. 101.000 m

  3. 99.000 m

  4. 96.790 m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Height of Instrument (HI) = Elevation of Benchmark + Backsight. Since the staff is inverted, the reading is treated as negative: HI = 100.0 + (-2.105) = 97.895 m. Elevation of Plinth = HI - Foresight = 97.895 - 1.105 = 96.790 m.

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