Carry out profile levelling using auto level.

The purpose of talking levels on each side of a main line at right angles to that line in order to determine a vertical cross-section of the surface of the ground, is known as:
A method of levelling in which the difference in elevation between two points is accurately determined by two sets of reciprocal observations when it is not possible to set up the level between the two points is known as:
While viewing through a level telescope and moving the eye slightly, a relative movement occurs between the image of the levelling staff and the cross hairs. The instrument is:
Levelling deals with measurements in a ______
Which line is the tangential to the level line at a point ?