The following readings were obtained during differential levelling. Reduced Level (RL) of point A is 240,000 m. The fore sight and back sight between points A and TPI is 1.420 m and 2.024 m, respectively. Fore sight and back sight between points TPI and TP2 is 2.100 m and 1.986 m, respectively. The back sight from B is 1.722 m. These are marked on the given figure. What is the RL at turning point - 2 (TP2)? All values are in metres.
The following readings were obtained during differential levelling. Reduced Level (RL) of point A is 240,000 m. The fore sight and back sight between points A and TPI is 1.420 m and 2.024 m, respectively. Fore sight and back sight between points TPI and TP2 is 2.100 m and 1.986 m, respectively. The back sight from B is 1.722 m. These are marked on the given figure. What is the RL at turning point - 2 (TP2)? All values are in metres. Correct Answer 240.490 m
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
(HI)A = 240 + 2.024 = 242.024 m
(RL)TP1 = (HI)A - FS at A = 242.024 – 1.42 = 240.604 m
HI when instrument is between TP1 and TP2,(HI)1-2 = RL at TP1 + BS between TP1 and TP2
(HI)1-2 = 240.604 + 1.986 = 242.59 m
(RL)TP2 = (HI)1-2 - FS between TP1 and TP2 = 242.59 – 2.1 = 240.49 m
∴ The reduced level of TP2 is 240.49 m.