It employs the principle of plain surveying. It’s assumed which the distances calculated are smaller in comparison to the radius of earth and so the influence of earth’s curvature advert refraction could be disregarded.Datum or surface area refers back to the issue or area from which the levels of other details or planes are established.· Benc

The reciprocal levelling eradicates the error resulting from curvature and collimation. In addition it gets rid of the mistake as a result of line of collimation.Differential leveling is done when the space between two details is much more. In this method, quantity of inter stations can be found and instrument is shifted to every station and notice