Leveling refers to any of the various processes by which elevations of points or differences in elevation are determined.



surveyors taking levels

To measure the difference in height ( ∆ H) between two points A and B, vertical rods are set up at each of these two points and a level somewhere between them.
The height difference between A and B is the difference between the staff readings.
The leveling is opened and closed fro a known point.

Opening a level: it involves setting up the level  a known control point and taking the first staff reading while  the staff is held vertically at a benchmark.


Closing a level: After taking level, the last reading is taken on a staff while held vertically on a benchmark.
Once the elevation of a point is determined, that point can be used for determining the elevations of other points

Below are the common terms used in leveling: 


 Backsight (BS): first reading taken on a staff when the instrument is set up at a new station
Foresight (FS): last reading taken on a staff before the instrument is set up at a new station
Turning Point: A point at which you have established an elevation with FS and on which you will subsequently take a BS
Intermediate sight:  A foresight to a point at which you want to know the elevation but which will not be used as a turning point