Correct Answer - Option 4 : 96.790 m
Concept:
The height of the instrument is first established by means of taking sight towards the benchmark of known elevation.
- Height of instrument = R.L of bench mark + Back sight reading
- Elevation of station = Height of instrument - Fore sight reading
Calculation:
Given:
R.L of benchmark = 100.0 m, Back sight reading = - 2.105 m (staff is inverted)
Fore sight reading = 1.105
Height of instrument = 100 + (-2.105) = 97.895 m
Elevation of plinth = 97.895 - 1.105 = 96.790 m.