If the staff is not held vertical at a level¬ling station, the reduced level calculated from the observation would be A. true R.L. B. more than true R.L. C. less than true R.L. D. none of the above

The correct answer is C. less than true R.L.

If the staff is not held vertical at a levelling station, the reduced level calculated from the observation will be less than the true R.L. This is because the angle of sight from the instrument to the staff will be greater than the true vertical angle, and the vertical distance between the instrument and the staff will be underestimated.

The following is a brief explanation of each option:

• Option A: true R.L. This is the correct reduced level if the staff is held vertical.
• Option B: more than true R.L. This is not possible, as the reduced level cannot be greater than the true R.L.
• Option C: less than true R.L. This is the correct answer, as explained above.
• Option D: none of the above. This is not the correct answer, as one of the options must be correct.