Height of instrument (HI) is measured from the benchmark where the datum is located a few meters below the benchmark.

True

False

In differential levelling, the dumpy level must be exactly situated in the middle of the two points of observation.

True

False

(1) FALSE

Height of instrument

Height of instrument (H.I.) = Backsite (B.S.) + Elevation of benchmark (B.M.).

In survey leveling, the vertical height of the line of collimation of the instrument over the station above which it is centered, or above a specified datum level.

In spirit leveling, the vertical distance from datum to line of sight of the instrument.

In stadia leveling the height of center of transit above the station stake.

In differential leveling, the elevation of the line of sight of the telescope when the instrument is leveled.

(2) FALSE

Differential levelling

Differential leveling is the process of measuring vertical distances from a known elevation point to determine elevations of unknown points.

Dumpy levels

These are more basic levels often used in construction work. The telescope is rigidly attached to a 

single bubble and the assembly is adjusted either by means of a screwed ball-joint or by 

footscrews which are adjusted first in one direction, then at 90°