SSC JE Civil Engineering 23-Mar-2021 Shift 1 Paper

Concepts:
When staff is held vertically downward, then Height of instrument is
HI = Reduce Level (RL) + Staff Reading (SR)
Also, Reduce level of any other point on ground is calculated as:
RL = HI – BS/FS {BS is Back Sight and FS is Fore Sight}
Calculations:
RL of Point A = 240 m
HI at A = RL at A + BS at A
${\left(\mathrm{HI}\right)}_{\mathrm{A}}$ = 240 + 2.024 = 242.024 m
${\left(\mathrm{RL}\right)}_{\mathrm{TP}}2$ = ${\left(\mathrm{HI}\right)}_{\mathrm{A}}$ - FS at A = 242.024 – 1.42 = 240.604 m
HI when instrument is between TP1 and TP2,${\left(\mathrm{HI}\right)}_1-2$ = RL at TP1 + BS between TP1 and TP2
${\left(\mathrm{HI}\right)}_1-2$ = 240.604 + 1.986 = 242.59 m
${\left(\mathrm{RL}\right)}_{\mathrm{TP}}2$ = ${\left(\mathrm{HI}\right)}_1-2$ - FS between TP1 and TP2 = 242.59 – 2.1 = 240.49 m
∴ The reduced level of TP2 is 240.49 m.