Levelling And Contouring Practice Questions

Diference of staff reading at $P_{1}$ and Q When instrument is at P + Difference of staff $n=\frac{\text{readings at }P_{1} \text{ and }Q_{1}\text{ when instrument is at Q }}{2}$ $\Rightarrow h=\frac{(2.800-1.700)+(2.700-1.800)}{2}$ $\Rightarrow h=1$ $\therefore$ Reduced level of station, Q= Reduced level of P+h $=100.000+1=101.000 \mathrm{m}$

The first reading is always BS. The second reading is foresight because the instrument has been shifted after this reading which is evident from the low value of third reading. Since the instrument has been shifted the third reading is backlight again. Successively the fourth reading is foresight.