Ex24-1 In a tangential method of tacheometry two vanes were fixed 2 m apart, the lower vane being 0.5 m above the foot of the staff held vertical at station A. The vertical angles measured are +1° 12' and -1° 30'. find the horizontal distance of A and reduced level of A, if the R.L. of the observation station is 101.365 m and height of instrument is 1.230 m.

Figure Ex24-1

Solution :

Let D be the horizontal distance between the observation station P and staff point A. Then, from Figure Ex24.1,

V = D tana₁

s - V = D tana₁

Or, s = D tana₂ + D tana₁

Given, s = 2 m; a₁= 1° 30' & a₂ = 1° 12'

Therefore R.L. of A = 101.365 + 1.230 -1.11 - 0.5 = 100.985 m