Question

A bench mark has been established at the soffit of an ornamental arch at the known elevation of 100.0 m above mean 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

• A. 103.210 m
• B. 99.000 m
• C. 101.000 m
• D. 96.790 m

Answer 1

The correct option is D 96.790 m

Inverted staff is used for the back sight (BS)

So, height of instrument,

$\text{= Reduced level of bench mark - BS}$

$=100-2.105=97.895m$

Elevation of plinth,

$\text{= Height of instrument - Fore sight}$

$=97.895-1.105=96.790m$