59) The R.L, of the point A which is on the floor is 100 m and back sight reading on A is 2.455 m. If the foresight reading on the point B which is on the ceiling is 2.745 m, the R.L. of point B will be

60) As applied to staff readings, the corrections for curvature and refraction are respectively The above table shows a part of a level field book. The value of X should be

61) If the horizontal distance between the staff point and the point of observation is d, then the error due to curvature of earth is proportional to

62) Sensitiveness of a level tube is designated by

63) Which of the following statements is incorrect ?