Seven consecutive readings taken with a levelling instrument are 1.345, 1.525, 0.785, 1.105, 1.855, 2.005, and 1.985. If the instrument was shifted after the third and fifth readings, the readings recorded in the Back Sight (BS) column would be:

In levelling, the line of collimation is known as ___________.

In the Rise and Fall method of levelling, if the next staff reading is greater than the previous staff reading, it indicates:

Consider the following statements regarding reciprocal levelling: Reciprocal levelling eliminates the effect of: I. Errors due to earth's curvature II. Errors due to atmospheric refraction III. Mistakes in taking levelling staff readings IV. Error due to the line of collimation not being parallel to the bubble tube axis Which of these statements are correct?