If the staff is not held vertical at a level¬ling station, the reduced level calculated from the observation would be

Answer: Option C

In levelling, it is essential that the staff is held vertically at the observation point.

If the staff is tilted (not vertical), the horizontal distance between the instrument and the staff increases slightly.

This results in the levelling instrument recording a reading higher than it would if the staff were vertical.

Since the reading is higher, the calculated Reduced Level (R.L.) becomes lower than the actual or true R.L.

Therefore, a non-vertical staff leads to a reduced level that is less than the true reduced level.

Hence, the correct answer is Option C: less than true R.L.