Explain the principle of techeometry with the help of a neat sketch.

Principle of tacheometry is based on principle of similar triangle in which corresponding sides & altitudes are proportional The ratio of distance of base from apex and length of base is always constant.

In fig. Oa1a2, Ob1b2, Oc1c2 are all isosceles triangles where D1, D2, D3 are the distances of bases from the apices (distances of staff stations from instrumnt stations) and S1, S2, S3 are the lengths of the bases also called staff intercepts.

According to stated principle.

D1/S1 = D2/S2=D3/ S3=f/i=Constant

Where f=focal length of objective and i =stadia intercept