To establish a set of bench marks, each B.M. is also used as a turning point. Elevation of B.Ms are checked by terminating to a previously established bench mark or by returning to the initial bench mark. A line of levels that ends at the point of beginning is known as level net. The final observation in a level net is thus a foresight on the initial B.M. The elevation of each B.M. is to be kept checked within the prescribed limit of error.
Tale 13.4 Permissible limit of error in level net
Order |
Class |
Limit (mm) |
Remark |
First |
I |
 |
K is the distance in km |
II |
 |
||
Second |
I |
 |
|
II |
 |
||
Third |
 |