Case : 1 (When the line of sight is horizontal and staff is held Vertical) Example : 1

 

The Following are the reading were taken with a tacheometer on to a vertical staff calculate the tachometer constant

Horizontal Distance	Stadia hair reading (m)
40	0.915	1.110	1.315
60	1.860	2.160	2.460

=>

       D₁  = KS₁ + C ................................(1)

       D₂  = KS₂ + C ................................(2)

S₁ = 1.315- 0.915 = 0.400 m    

S2 = 2.460 – 1.860 = 0.600 m    

D₁ = KS₁ + C

40 = K (1.335 – 0.885) + C

40 = K (0.40) + C ....................(3)

D₂ = KS₂ + C

60 = K (2.460 – 1.860) + C

60 = K (0.6) + C

C = 60 - K (0.6)   ....................(4)

Now put the value of eq 4 in eq 3

  40 = K (0.40) + C ....................(3)

40 = K (0.40) + 60 - K (0.60)

40 – 60 = - 0.20 K

                         - 20 = - 0.20 K

K = 100

Put the value of K in Eq no 3

  40 = K (0.40) + C

40 = 100 (0.40) + C

C = 0