Levelling (or leveling in American spelling) is a branch of surveying, the object of which is to
- Find the elevation of a given point with respect to the given or assumed Datum.
- Establish a point at a given elevation with respect to the given or assumed Datum.
Levelling is the measurement of geodetic height using an optical levelling instrument and a level staff or rod having a numbered scale. Common levelling instruments include the spirit level, the dumpy level, the digital level, and the laser level.
Read more about Levelling: Spirit (Optical) Levelling, Leveling Procedure, Refraction and Curvature, Leveling Loops and Gravity Variations