radius of level tube

length of level tube

length of bubble of level tube

none of the above

Error due to refraction may not be completely eliminated by reciprocal levelling.

Tilting levels are commonly used for precision work.

The last reading of levelling is always a foresight.

All of the above statements are incorrect.

the instrument is to be shifted frequently

fly levelling is being done over long distance

many readings are to be taken from a single setting of the instrument

all of the above

equidistant from A and B

closer to the higher station

closer to the lower station

as far as possible from the line AB

inversely proportional to the scale of the map

directly proportional to the flatness of ground

larger for accurate works

larger if the time available is more