Which one of the following statements is correct ? A. when the axes of rotation of the graduated circle and the verniers are not coincident, the instrument possesses eccentricity B. the mean of the readings of the two verniers gives correct reading free from the eccentricity C. one vernier may be used if the readings of two verniers differ by a constant D. all the above. A. when the axes of rotation of the graduated circle and the verniers are not coincident, the instrument possesses eccentricity B. the mean of the readings of the two verniers gives correct reading free from the eccentricity C. one vernier may be used if the readings of two verniers differ by a constant D. all the above.