29) What is the term of sight, if the sight taken between the back sight and fore sight on a levelling staff held over a point of unknown elevations?

30) What is the level that combine good features both the dumpy level and 'y' level?

31) What is the fundamental line in levels?

32) Which levelling instrument is required in second adjustment to make the line of collimation parallel to the axis of the bubble tube?

33) Which level instrument requires a signal permanent adjustment?