The following readings were obtained during differential levelling.
The reduced Level (RL) of point A is 240.000 m. The foresight and back sight between points A and TPI is 1.420 m and 2.024 m, respectively. Fore sight and back sight between points TP1 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 meters.
The operation of levelling to determine the elevation of points at some distance apart is called differential levelling and is usually accomplished by direct levelling.
Start with A (+ve for up and –ve for down)
Elevation of TP2 compare to A
= +2.024 + (1.986 – 1.42) – 2.1
= + 0.49
∴ RL of TP2 = 240 + 0.49 = 240.49 m