Question

A levelling reading is taken as 2.25 m. The line of sight has a deflection of 20 cm relative to the vertical position of the staff. Find the correct reading (rounded to two decimals).

Hint:

In levelling, if the staff leans towards the instrument, the reading increases; hence subtract the deflection amount.

Answer 1

Correct Answer: 2.2

A 20 cm = 0.20 m deflection means the vertical reading is shorter than the observed reading by 0.20 m. Correct reading: \[ R_{\text{true}} = R_{\text{observed}} - 0.20 \] \[ R_{\text{true}} = 2.25 - 0.20 = 2.05\ \text{m} \] Rounded to two decimals: \[ \boxed{2.05\ \text{m}} \]