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WHAT IS THE RECIPROCAL LEVELING





What Is Reciprocal Leveling



Reciprocal Leveling is a method of levelling to determine the difference of level between two points at a considerable distance apart with great precision.

Reciprocal Leveling is also used when it is not possible to set up a level instrument.

 WHAT -IS- THE -RECIPROCAL- LEVELING
fig 1.


PROCEDURE
Let A and B be the two points whose difference is to be determined.


i. Set the level instrument near A. Complete temporary adjustment and takes reading staff A and B. Write the reading like as a1 and b1. shown in fig. 1

 WHAT- IS- THE- RECIPROCAL- LEVELING
fig 2.


ii Transfer the instrument to B and set up near to B. Make a temporary adjustment. Take the staff reading as a2 and b2.






d= the true difference of level between A and B.
e= the total error due to curvature, refraction, and imperfect collimation adjustment.


The correct staff reading in fig.1= b1-e.


The correct staff reading in fig.2= a2-e.


In the fig.1 the true difference of level between A and B (true fall from A to B)
d= (b1-e)-a1 




or d= (b1-a1)-e  ....................................equation F


In the fig.2 the true difference  of level between A and B (true fall from A to B)


d= b2-(a2-e) or
(b2-a2) +e  ............................................equation G


 Adding the equation Fand G to eliminate e, we get


d= (b1-a1)+(b2-a2)/2


Two values gives the true difference of elevation between two points free from all errors, like error due to curvature of the earth, refraction error and error of collimation error.