Correct Answer - Option 3 : L(sec x - 1)
Explanation:
L = Staff Reading
X = Angle of inclination
So, if staff is vertical then reading on staff = L
if staff kept at an angle X then reading on staff = L sec X
Error due to non-verticallity of the staff = Measured value - True Value
Error due to non-verticallity of the staff = L sec X - L
Error due to non-verticallity of the staff = L (sec X - 1)